| Message ID | 20241028163403.522001-1-eugen.hristev@linaro.org (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v2] soc: qcom: Rework BCM_TCS_CMD macro | expand |
Quoting Eugen Hristev (2024-10-28 09:34:03) > diff --git a/include/soc/qcom/tcs.h b/include/soc/qcom/tcs.h > index 3acca067c72b..152947a922c0 100644 > --- a/include/soc/qcom/tcs.h > +++ b/include/soc/qcom/tcs.h > @@ -60,22 +63,19 @@ struct tcs_request { > struct tcs_cmd *cmds; > }; > > -#define BCM_TCS_CMD_COMMIT_SHFT 30 > -#define BCM_TCS_CMD_COMMIT_MASK 0x40000000 > -#define BCM_TCS_CMD_VALID_SHFT 29 > -#define BCM_TCS_CMD_VALID_MASK 0x20000000 > -#define BCM_TCS_CMD_VOTE_X_SHFT 14 > -#define BCM_TCS_CMD_VOTE_MASK 0x3fff > -#define BCM_TCS_CMD_VOTE_Y_SHFT 0 > -#define BCM_TCS_CMD_VOTE_Y_MASK 0xfffc000 > +#define BCM_TCS_CMD_COMMIT_MASK BIT(30) > +#define BCM_TCS_CMD_VALID_MASK BIT(29) > +#define BCM_TCS_CMD_VOTE_MASK GENMASK(13, 0) > +#define BCM_TCS_CMD_VOTE_Y_MASK GENMASK(13, 0) > +#define BCM_TCS_CMD_VOTE_X_MASK GENMASK(27, 14) > > /* Construct a Bus Clock Manager (BCM) specific TCS command */ > #define BCM_TCS_CMD(commit, valid, vote_x, vote_y) \ > - (((commit) << BCM_TCS_CMD_COMMIT_SHFT) | \ > - ((valid) << BCM_TCS_CMD_VALID_SHFT) | \ > - ((cpu_to_le32(vote_x) & \ > - BCM_TCS_CMD_VOTE_MASK) << BCM_TCS_CMD_VOTE_X_SHFT) | \ > - ((cpu_to_le32(vote_y) & \ > - BCM_TCS_CMD_VOTE_MASK) << BCM_TCS_CMD_VOTE_Y_SHFT)) > + (le32_encode_bits(commit, BCM_TCS_CMD_COMMIT_MASK) | \ > + le32_encode_bits(valid, BCM_TCS_CMD_VALID_MASK) | \ > + le32_encode_bits(vote_x, \ > + BCM_TCS_CMD_VOTE_X_MASK) | \ > + le32_encode_bits(vote_y, \ > + BCM_TCS_CMD_VOTE_Y_MASK)) Why is cpu_to_le32() inside BCM_TCS_CMD at all? Is struct tcs_cmd::data supposed to be marked as __le32? Can the whole u32 be constructed and turned into an __le32 after setting all the bit fields instead of using le32_encode_bits() multiple times?
On 10/28/24 19:56, Stephen Boyd wrote: > Quoting Eugen Hristev (2024-10-28 09:34:03) >> diff --git a/include/soc/qcom/tcs.h b/include/soc/qcom/tcs.h >> index 3acca067c72b..152947a922c0 100644 >> --- a/include/soc/qcom/tcs.h >> +++ b/include/soc/qcom/tcs.h >> @@ -60,22 +63,19 @@ struct tcs_request { >> struct tcs_cmd *cmds; >> }; >> >> -#define BCM_TCS_CMD_COMMIT_SHFT 30 >> -#define BCM_TCS_CMD_COMMIT_MASK 0x40000000 >> -#define BCM_TCS_CMD_VALID_SHFT 29 >> -#define BCM_TCS_CMD_VALID_MASK 0x20000000 >> -#define BCM_TCS_CMD_VOTE_X_SHFT 14 >> -#define BCM_TCS_CMD_VOTE_MASK 0x3fff >> -#define BCM_TCS_CMD_VOTE_Y_SHFT 0 >> -#define BCM_TCS_CMD_VOTE_Y_MASK 0xfffc000 >> +#define BCM_TCS_CMD_COMMIT_MASK BIT(30) >> +#define BCM_TCS_CMD_VALID_MASK BIT(29) >> +#define BCM_TCS_CMD_VOTE_MASK GENMASK(13, 0) >> +#define BCM_TCS_CMD_VOTE_Y_MASK GENMASK(13, 0) >> +#define BCM_TCS_CMD_VOTE_X_MASK GENMASK(27, 14) >> >> /* Construct a Bus Clock Manager (BCM) specific TCS command */ >> #define BCM_TCS_CMD(commit, valid, vote_x, vote_y) \ >> - (((commit) << BCM_TCS_CMD_COMMIT_SHFT) | \ >> - ((valid) << BCM_TCS_CMD_VALID_SHFT) | \ >> - ((cpu_to_le32(vote_x) & \ >> - BCM_TCS_CMD_VOTE_MASK) << BCM_TCS_CMD_VOTE_X_SHFT) | \ >> - ((cpu_to_le32(vote_y) & \ >> - BCM_TCS_CMD_VOTE_MASK) << BCM_TCS_CMD_VOTE_Y_SHFT)) >> + (le32_encode_bits(commit, BCM_TCS_CMD_COMMIT_MASK) | \ >> + le32_encode_bits(valid, BCM_TCS_CMD_VALID_MASK) | \ >> + le32_encode_bits(vote_x, \ >> + BCM_TCS_CMD_VOTE_X_MASK) | \ >> + le32_encode_bits(vote_y, \ >> + BCM_TCS_CMD_VOTE_Y_MASK)) > > Why is cpu_to_le32() inside BCM_TCS_CMD at all? Is struct tcs_cmd::data > supposed to be marked as __le32? > > Can the whole u32 be constructed and turned into an __le32 after setting > all the bit fields instead of using le32_encode_bits() multiple times? I believe no. The fields inside the constructed TCS command should be little endian. If we construct the whole u32 and then convert it from cpu endinaness to little endian, this might prove to be incorrect as it would swap the bytes at the u32 level, while originally, the bytes for each field that was longer than 1 byte were swapped before being added to the constructed u32. So I would say that the fields inside the constructed item are indeed le32, but the result as a whole is an u32 which would be sent to the hardware using an u32 container , and no byte swapping should be done there, as the masks already place the fields at the required offsets. So the tcs_cmd.data is not really a le32, at least my acception of it. Does this make sense ? Eugen
Quoting Eugen Hristev (2024-10-29 06:12:12) > On 10/28/24 19:56, Stephen Boyd wrote: > > Quoting Eugen Hristev (2024-10-28 09:34:03) > >> diff --git a/include/soc/qcom/tcs.h b/include/soc/qcom/tcs.h > >> index 3acca067c72b..152947a922c0 100644 > >> --- a/include/soc/qcom/tcs.h > >> +++ b/include/soc/qcom/tcs.h [....] > >> /* Construct a Bus Clock Manager (BCM) specific TCS command */ > >> #define BCM_TCS_CMD(commit, valid, vote_x, vote_y) \ > >> - (((commit) << BCM_TCS_CMD_COMMIT_SHFT) | \ > >> - ((valid) << BCM_TCS_CMD_VALID_SHFT) | \ > >> - ((cpu_to_le32(vote_x) & \ > >> - BCM_TCS_CMD_VOTE_MASK) << BCM_TCS_CMD_VOTE_X_SHFT) | \ > >> - ((cpu_to_le32(vote_y) & \ > >> - BCM_TCS_CMD_VOTE_MASK) << BCM_TCS_CMD_VOTE_Y_SHFT)) > >> + (le32_encode_bits(commit, BCM_TCS_CMD_COMMIT_MASK) | \ > >> + le32_encode_bits(valid, BCM_TCS_CMD_VALID_MASK) | \ > >> + le32_encode_bits(vote_x, \ > >> + BCM_TCS_CMD_VOTE_X_MASK) | \ > >> + le32_encode_bits(vote_y, \ > >> + BCM_TCS_CMD_VOTE_Y_MASK)) > > > > Why is cpu_to_le32() inside BCM_TCS_CMD at all? Is struct tcs_cmd::data > > supposed to be marked as __le32? > > > > Can the whole u32 be constructed and turned into an __le32 after setting > > all the bit fields instead of using le32_encode_bits() multiple times? > > I believe no. The fields inside the constructed TCS command should be > little endian. If we construct the whole u32 and then convert it from > cpu endinaness to little endian, this might prove to be incorrect as it > would swap the bytes at the u32 level, while originally, the bytes for > each field that was longer than 1 byte were swapped before being added > to the constructed u32. > So I would say that the fields inside the constructed item are indeed > le32, but the result as a whole is an u32 which would be sent to the > hardware using an u32 container , and no byte swapping should be done > there, as the masks already place the fields at the required offsets. > So the tcs_cmd.data is not really a le32, at least my acception of it. > Does this make sense ? > Sort of? But I thought that the RPMh hardware was basically 32-bit little-endian registers. That's why write_tcs_*() APIs in drivers/soc/qcom/rpmh-rsc.c use writel() and readl(), right? The cpu_to_le32() code that's there today is doing nothing, because the CPU is little-endian 99% of the time. It's likely doing the wrong thing on big-endian machines. Looking at commit 6311b6521bcc ("drivers: qcom: Add BCM vote macro to header") it seems to have picked the macro version from interconnect vs. clk subsystem. And commit b5d2f741077a ("interconnect: qcom: Add sdm845 interconnect provider driver") used cpu_to_le32() but I can't figure out why. If the rpmh-rsc code didn't use writel() or readl() I'd believe that the data member is simply a u32 container. But those writel() and readl() functions are doing a byte swap, which seems to imply that the data member is a native CPU endian u32 that needs to be converted to little-endian. Sounds like BCM_TCS_CMD() should just pack things into a u32 and we can simply remove the cpu_to_l32() stuff in the macro?
On 10/30/24 02:40, Stephen Boyd wrote: > Quoting Eugen Hristev (2024-10-29 06:12:12) >> On 10/28/24 19:56, Stephen Boyd wrote: >>> Quoting Eugen Hristev (2024-10-28 09:34:03) >>>> diff --git a/include/soc/qcom/tcs.h b/include/soc/qcom/tcs.h >>>> index 3acca067c72b..152947a922c0 100644 >>>> --- a/include/soc/qcom/tcs.h >>>> +++ b/include/soc/qcom/tcs.h > [....] >>>> /* Construct a Bus Clock Manager (BCM) specific TCS command */ >>>> #define BCM_TCS_CMD(commit, valid, vote_x, vote_y) \ >>>> - (((commit) << BCM_TCS_CMD_COMMIT_SHFT) | \ >>>> - ((valid) << BCM_TCS_CMD_VALID_SHFT) | \ >>>> - ((cpu_to_le32(vote_x) & \ >>>> - BCM_TCS_CMD_VOTE_MASK) << BCM_TCS_CMD_VOTE_X_SHFT) | \ >>>> - ((cpu_to_le32(vote_y) & \ >>>> - BCM_TCS_CMD_VOTE_MASK) << BCM_TCS_CMD_VOTE_Y_SHFT)) >>>> + (le32_encode_bits(commit, BCM_TCS_CMD_COMMIT_MASK) | \ >>>> + le32_encode_bits(valid, BCM_TCS_CMD_VALID_MASK) | \ >>>> + le32_encode_bits(vote_x, \ >>>> + BCM_TCS_CMD_VOTE_X_MASK) | \ >>>> + le32_encode_bits(vote_y, \ >>>> + BCM_TCS_CMD_VOTE_Y_MASK)) >>> >>> Why is cpu_to_le32() inside BCM_TCS_CMD at all? Is struct tcs_cmd::data >>> supposed to be marked as __le32? >>> >>> Can the whole u32 be constructed and turned into an __le32 after setting >>> all the bit fields instead of using le32_encode_bits() multiple times? >> >> I believe no. The fields inside the constructed TCS command should be >> little endian. If we construct the whole u32 and then convert it from >> cpu endinaness to little endian, this might prove to be incorrect as it >> would swap the bytes at the u32 level, while originally, the bytes for >> each field that was longer than 1 byte were swapped before being added >> to the constructed u32. >> So I would say that the fields inside the constructed item are indeed >> le32, but the result as a whole is an u32 which would be sent to the >> hardware using an u32 container , and no byte swapping should be done >> there, as the masks already place the fields at the required offsets. >> So the tcs_cmd.data is not really a le32, at least my acception of it. >> Does this make sense ? >> > > Sort of? But I thought that the RPMh hardware was basically 32-bit > little-endian registers. That's why write_tcs_*() APIs in > drivers/soc/qcom/rpmh-rsc.c use writel() and readl(), right? The > cpu_to_le32() code that's there today is doing nothing, because the CPU > is little-endian 99% of the time. It's likely doing the wrong thing on > big-endian machines. Looking at commit 6311b6521bcc ("drivers: qcom: Add > BCM vote macro to header") it seems to have picked the macro version > from interconnect vs. clk subsystem. And commit b5d2f741077a > ("interconnect: qcom: Add sdm845 interconnect provider driver") used > cpu_to_le32() but I can't figure out why. > > If the rpmh-rsc code didn't use writel() or readl() I'd believe that the > data member is simply a u32 container. But those writel() and readl() > functions are doing a byte swap, which seems to imply that the data > member is a native CPU endian u32 that needs to be converted to > little-endian. Sounds like BCM_TCS_CMD() should just pack things into a > u32 and we can simply remove the cpu_to_l32() stuff in the macro? This review [1] from Evan Green on the original patch submission requested the use of cpu_to_le32 So that's how it ended up there. [1] https://lore.kernel.org/linux-kernel//20180806225252.GQ30024@minitux/T/#mab6b799b3f9b51725c804a65f3580ef8894205f2
Quoting Eugen Hristev (2024-10-30 01:28:14) > On 10/30/24 02:40, Stephen Boyd wrote: > > > > If the rpmh-rsc code didn't use writel() or readl() I'd believe that the > > data member is simply a u32 container. But those writel() and readl() > > functions are doing a byte swap, which seems to imply that the data > > member is a native CPU endian u32 that needs to be converted to > > little-endian. Sounds like BCM_TCS_CMD() should just pack things into a > > u32 and we can simply remove the cpu_to_l32() stuff in the macro? > > This review [1] from Evan Green on the original patch submission > requested the use of cpu_to_le32 > > So that's how it ended up there. > Thanks. I still don't see why this can't just be treated as a u32 and then we have writel() take care of it for us.
On 11/8/24 21:00, Stephen Boyd wrote: > Quoting Eugen Hristev (2024-10-30 01:28:14) >> On 10/30/24 02:40, Stephen Boyd wrote: >>> >>> If the rpmh-rsc code didn't use writel() or readl() I'd believe >>> that the data member is simply a u32 container. But those >>> writel() and readl() functions are doing a byte swap, which >>> seems to imply that the data member is a native CPU endian u32 >>> that needs to be converted to little-endian. Sounds like >>> BCM_TCS_CMD() should just pack things into a u32 and we can >>> simply remove the cpu_to_l32() stuff in the macro? >> >> This review [1] from Evan Green on the original patch submission >> requested the use of cpu_to_le32 >> >> So that's how it ended up there. >> > > Thanks. I still don't see why this can't just be treated as a u32 > and then we have writel() take care of it for us. If the values are in the wrong endianness, e.g. 0xff11 instead of 0x11ff, the corresponding field would be filled up wrongly, even possibly writing unwanted bits. vote_x and vote_y have a mask of length 14, so there is one byte and another 6 more bits. If the endianness of the value is not correct, the one byte might end up written over the 6 bits and 2 extra bits which are supposed to be for another field. In my example 0x11 should be in the first 6 bits and the 0xff in the next byte, but if the endianness of the cpu is different, we might write 0xff on the 6 bit field. So we must ensure that the multi-byte fields are in the correct endianness that the hardware expects. In other words, writel does not know about the multi-byte fields inside this u32 which have a specific bit shift, and those fields are expected to be in le32 order written to the hardware. Whether or not the cpu is le32 is not important because using cpu_to_le32 will make it safe either way. I apologize for my not so great explanation
Quoting Eugen Hristev (2024-11-11 05:05:02) > > > On 11/8/24 21:00, Stephen Boyd wrote: > > Quoting Eugen Hristev (2024-10-30 01:28:14) > >> On 10/30/24 02:40, Stephen Boyd wrote: > >>> > >>> If the rpmh-rsc code didn't use writel() or readl() I'd believe > >>> that the data member is simply a u32 container. But those > >>> writel() and readl() functions are doing a byte swap, which > >>> seems to imply that the data member is a native CPU endian u32 > >>> that needs to be converted to little-endian. Sounds like > >>> BCM_TCS_CMD() should just pack things into a u32 and we can > >>> simply remove the cpu_to_l32() stuff in the macro? > >> > >> This review [1] from Evan Green on the original patch submission > >> requested the use of cpu_to_le32 > >> > >> So that's how it ended up there. > >> > > > > Thanks. I still don't see why this can't just be treated as a u32 > > and then we have writel() take care of it for us. > > If the values are in the wrong endianness, e.g. 0xff11 instead of > 0x11ff, the corresponding field would be filled up wrongly, even > possibly writing unwanted bits. vote_x and vote_y have a mask of length > 14, so there is one byte and another 6 more bits. If the endianness of > the value is not correct, the one byte might end up written over the 6 > bits and 2 extra bits which are supposed to be for another field. > In my example 0x11 should be in the first 6 bits and the 0xff in the > next byte, but if the endianness of the cpu is different, we might write > 0xff on the 6 bit field. > So we must ensure that the multi-byte fields are in the correct > endianness that the hardware expects. The vote_x field looks like it goes from bits 14 to 27. No matter the endian format of the _word_, bits 14 to 27 are for the vote_x field. So if I set bit 15 and 17 in a big-endian format word (vote_x is decimal 10), pass that 32-bit word to writel(), swap the bytes, it is still set as bit 15 and 17 in little-endian format. That's because when I read the 32-bit word as a little-endian machine, the first byte is for bits 0 to 7, second byte is for bits 8 to 15, third byte is for 16 to 23, and fourth byte is for bits 24 to 31. The hardware assembles the 32-bit word out of that byte order, knowing that bits are mapped that way. Once I have the 32-bit word, it can be shifted right 14 times so that the vote_x field is from 0 to 13, and bits 1 and 3 are set, i.e. decimal 10. Fields that span bytes don't matter here. The hardware is going to read the word in the format that it is in, which is the order of bytes, and assemble a full 32-bit word out of it. We're just setting bits in the field that's shifted so many bits because it's part of a word. The order of the bits isn't changing. > > In other words, writel does not know about the multi-byte fields inside > this u32 which have a specific bit shift, and those fields are expected > to be in le32 order written to the hardware. Whether or not the cpu is > le32 is not important because using cpu_to_le32 will make it safe either > way. > > I apologize for my not so great explanation > I hope my explanation has helped. Long story short, the cpu_to_le32() usage here is wrong. Typically we try to operate with a type that's the same size and native format for as long as possible (u32), partially for performance reasons but also to make it easier to understand. When it comes time to write that value to the hardware, write it in the hardware format (writel), and read from the hardware in the hardware format (readl). Doing this lets you avoid thinking about the endianness almost entirely, and makes it so that code doesn't have to be rewritten when running on a different endian CPU to avoid suffering performance penalties with all the byte swapping.
diff --git a/drivers/clk/qcom/clk-rpmh.c b/drivers/clk/qcom/clk-rpmh.c index 4acde937114a..4929893b09c2 100644 --- a/drivers/clk/qcom/clk-rpmh.c +++ b/drivers/clk/qcom/clk-rpmh.c @@ -267,7 +267,7 @@ static int clk_rpmh_bcm_send_cmd(struct clk_rpmh *c, bool enable) if (c->last_sent_aggr_state != cmd_state) { cmd.addr = c->res_addr; - cmd.data = BCM_TCS_CMD(1, enable, 0, cmd_state); + cmd.data = (__force u32)BCM_TCS_CMD(1, enable, 0, cmd_state); /* * Send only an active only state request. RPMh continues to diff --git a/drivers/interconnect/qcom/bcm-voter.c b/drivers/interconnect/qcom/bcm-voter.c index a2d437a05a11..ce9091cf122b 100644 --- a/drivers/interconnect/qcom/bcm-voter.c +++ b/drivers/interconnect/qcom/bcm-voter.c @@ -144,7 +144,7 @@ static inline void tcs_cmd_gen(struct tcs_cmd *cmd, u64 vote_x, u64 vote_y, vote_y = BCM_TCS_CMD_VOTE_MASK; cmd->addr = addr; - cmd->data = BCM_TCS_CMD(commit, valid, vote_x, vote_y); + cmd->data = (__force u32)BCM_TCS_CMD(commit, valid, vote_x, vote_y); /* * Set the wait for completion flag on command that need to be completed diff --git a/include/soc/qcom/tcs.h b/include/soc/qcom/tcs.h index 3acca067c72b..152947a922c0 100644 --- a/include/soc/qcom/tcs.h +++ b/include/soc/qcom/tcs.h @@ -6,6 +6,9 @@ #ifndef __SOC_QCOM_TCS_H__ #define __SOC_QCOM_TCS_H__ +#include <linux/bitfield.h> +#include <linux/bits.h> + #define MAX_RPMH_PAYLOAD 16 /** @@ -60,22 +63,19 @@ struct tcs_request { struct tcs_cmd *cmds; }; -#define BCM_TCS_CMD_COMMIT_SHFT 30 -#define BCM_TCS_CMD_COMMIT_MASK 0x40000000 -#define BCM_TCS_CMD_VALID_SHFT 29 -#define BCM_TCS_CMD_VALID_MASK 0x20000000 -#define BCM_TCS_CMD_VOTE_X_SHFT 14 -#define BCM_TCS_CMD_VOTE_MASK 0x3fff -#define BCM_TCS_CMD_VOTE_Y_SHFT 0 -#define BCM_TCS_CMD_VOTE_Y_MASK 0xfffc000 +#define BCM_TCS_CMD_COMMIT_MASK BIT(30) +#define BCM_TCS_CMD_VALID_MASK BIT(29) +#define BCM_TCS_CMD_VOTE_MASK GENMASK(13, 0) +#define BCM_TCS_CMD_VOTE_Y_MASK GENMASK(13, 0) +#define BCM_TCS_CMD_VOTE_X_MASK GENMASK(27, 14) /* Construct a Bus Clock Manager (BCM) specific TCS command */ #define BCM_TCS_CMD(commit, valid, vote_x, vote_y) \ - (((commit) << BCM_TCS_CMD_COMMIT_SHFT) | \ - ((valid) << BCM_TCS_CMD_VALID_SHFT) | \ - ((cpu_to_le32(vote_x) & \ - BCM_TCS_CMD_VOTE_MASK) << BCM_TCS_CMD_VOTE_X_SHFT) | \ - ((cpu_to_le32(vote_y) & \ - BCM_TCS_CMD_VOTE_MASK) << BCM_TCS_CMD_VOTE_Y_SHFT)) + (le32_encode_bits(commit, BCM_TCS_CMD_COMMIT_MASK) | \ + le32_encode_bits(valid, BCM_TCS_CMD_VALID_MASK) | \ + le32_encode_bits(vote_x, \ + BCM_TCS_CMD_VOTE_X_MASK) | \ + le32_encode_bits(vote_y, \ + BCM_TCS_CMD_VOTE_Y_MASK)) #endif /* __SOC_QCOM_TCS_H__ */
Reworked BCM_TCS_CMD macro in order to fix warnings from sparse: drivers/clk/qcom/clk-rpmh.c:270:28: warning: restricted __le32 degrades to integer drivers/clk/qcom/clk-rpmh.c:270:28: warning: restricted __le32 degrades to integer While at it, used le32_encode_bits which made the code easier to follow and removed unnecessary shift definitions. Signed-off-by: Eugen Hristev <eugen.hristev@linaro.org> --- drivers/clk/qcom/clk-rpmh.c | 2 +- drivers/interconnect/qcom/bcm-voter.c | 2 +- include/soc/qcom/tcs.h | 28 +++++++++++++-------------- 3 files changed, 16 insertions(+), 16 deletions(-)