| Message ID | 1523172498-74798-1-git-send-email-shawn.lin@rock-chips.com (mailing list archive) |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
Hi Michael and Stephen Any chance to take a look at this patch? :) On 2018/4/8 15:28, Shawn Lin wrote: > CLK_DIVIDER_EVEN is used for clock divders that should only > use even number in the div field. > > Two clock divder should consider to use this flag > (1) The divder is physically only support even div number to > generate 50% duty cycle clock rate. > (2) The divder's clock consumer request it to use even div number > to generate the most closest requested rate for whatever reason. > > In some platforms, for instance Rockchip, the eMMC/SDIO/SDMMC should > request divder to use even number when working at a high throughput > speed mode reliably. However, that wasn't guaranteed by clock framework. > So the previous tricky is to carefully assign magic clock rate to their > parents as well as consumer's clock rate when requesting. That works > bad in practice if folks change the parents clock rate or the clock > hierarchy randomly. That also work bad if the consumer's clock rate > came from the DT, which is changed so fraquent for different boards. > > To make it's less prone to make mistake and to make it really respect > the fact that the divder should use even number to the div field, we > need the clock framework's help. Now we have CLK_DIVIDER_POWER_OF_TWO, > which could guarantee the div field is even number, however, obviously > it skips the even numbers which isn't the power of 2, but maybe which is > the best div to generate closest clock rate for consumer. > > Look at the examples here when doing some random test on Rockchip's > platforms, by changing the requested clock rate from DT, namely > assigning different max-frquency for MMC node, > > when the mmc host driver requests 80MHz with CLK_DIVIDER_POWER_OF_TWO > flag for the clock divder, it shows the final clock rate is 61.44Mhz > > pll_vpll0 1 1 983039999 0 0 > vpll0 4 4 983039999 0 0 > clk_emmc_div 1 1 122880000 0 0 > clk_emmc 1 1 122880000 0 0 > emmc_sample 0 0 61440000 0 155 > emmc_drv 0 0 61440000 0 180 > > With this patch and add CLK_DIVIDER_EVEN flag for clk_emmc_div, we get > the final clock rate, 67.7376MHz. > > pll_vpll1 1 1 812851199 0 0 > vpll1 2 2 812851199 0 0 > clk_emmc_div 1 1 135475200 0 0 > clk_emmc 1 1 135475200 0 0 > emmc_sample 0 0 67737600 0 113 > emmc_drv 0 0 67737600 0 180 > > Apprently 67737600 is better than 61440000 when requesting 80MHz. > Of course, we could have more case that worsen the gap between > the desired rate and the actual rate if using CLK_DIVIDER_POWER_OF_TWO. > > Alternatively, clk_div_table could be resorted to handle different kinds > of div limilation, and it seems to be applied to irregular div calculation > in practice by current clock provider drivers, but even number for div > field is a rather common, regular and symmetrical requirement. So it is > worth to introduces CLK_DIVIDER_EVEN flag for clock framework to make > the best in this process. > > Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com> > > --- > > Changes in v3: > - Fix a wrong if condition check > > Changes in v2: > - Avoid to use div 1 if (CLK_DIVIDER_EVEN | CLK_DIVIDER_POWER_OF_TWO) > suggested by Heiko. And seems actually no other flags should be bothered > by this newly added CLK_DIVIDER_EVEN. > > drivers/clk/clk-divider.c | 26 ++++++++++++++++++++++++-- > include/linux/clk-provider.h | 3 +++ > 2 files changed, 27 insertions(+), 2 deletions(-) > > diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c > index b6234a5..8f305f1 100644 > --- a/drivers/clk/clk-divider.c > +++ b/drivers/clk/clk-divider.c > @@ -159,8 +159,17 @@ static bool _is_valid_table_div(const struct clk_div_table *table, > static bool _is_valid_div(const struct clk_div_table *table, unsigned int div, > unsigned long flags) > { > - if (flags & CLK_DIVIDER_POWER_OF_TWO) > - return is_power_of_2(div); > + bool is_valid; > + > + if (flags & CLK_DIVIDER_POWER_OF_TWO) { > + is_valid = is_power_of_2(div); > + if (flags & CLK_DIVIDER_EVEN) > + return is_valid && (div != 1); > + return is_valid; > + } > + > + if (flags & CLK_DIVIDER_EVEN) > + return !(div % 2); > if (table) > return _is_valid_table_div(table, div); > return true; > @@ -208,6 +217,12 @@ static int _div_round_up(const struct clk_div_table *table, > { > int div = DIV_ROUND_UP_ULL((u64)parent_rate, rate); > > + /* > + * Check even before power of two to avoid div 1 if combination > + * happens, which applies to all the following similarities. > + */ > + if (flags & CLK_DIVIDER_EVEN) > + div = !(div % 2) ? div : (div + 1); > if (flags & CLK_DIVIDER_POWER_OF_TWO) > div = __roundup_pow_of_two(div); > if (table) > @@ -226,6 +241,11 @@ static int _div_round_closest(const struct clk_div_table *table, > up = DIV_ROUND_UP_ULL((u64)parent_rate, rate); > down = parent_rate / rate; > > + if (flags & CLK_DIVIDER_EVEN) { > + up = !(up % 2) ? up : (up + 1); > + down = !(down % 2) ? down : (down - 1); > + } > + > if (flags & CLK_DIVIDER_POWER_OF_TWO) { > up = __roundup_pow_of_two(up); > down = __rounddown_pow_of_two(down); > @@ -264,6 +284,8 @@ static int _next_div(const struct clk_div_table *table, int div, > { > div++; > > + if (flags & CLK_DIVIDER_EVEN) > + div = !(div % 2) ? div : (div + 1); > if (flags & CLK_DIVIDER_POWER_OF_TWO) > return __roundup_pow_of_two(div); > if (table) > diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h > index 210a890..7c59611 100644 > --- a/include/linux/clk-provider.h > +++ b/include/linux/clk-provider.h > @@ -388,6 +388,8 @@ struct clk_div_table { > * CLK_DIVIDER_MAX_AT_ZERO - For dividers which are like CLK_DIVIDER_ONE_BASED > * except when the value read from the register is zero, the divisor is > * 2^width of the field. > + * CLK_DIVIDER_EVEN - For the dividers which could only use even number in the > + * div field. > */ > struct clk_divider { > struct clk_hw hw; > @@ -409,6 +411,7 @@ struct clk_divider { > #define CLK_DIVIDER_ROUND_CLOSEST BIT(4) > #define CLK_DIVIDER_READ_ONLY BIT(5) > #define CLK_DIVIDER_MAX_AT_ZERO BIT(6) > +#define CLK_DIVIDER_EVEN BIT(7) > > extern const struct clk_ops clk_divider_ops; > extern const struct clk_ops clk_divider_ro_ops; > -- To unsubscribe from this list: send the line "unsubscribe linux-clk" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Quoting Shawn Lin (2018-05-25 01:37:39) > Ping.... :) > This is old. Please resend and we can reconsider.
diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c index b6234a5..8f305f1 100644 --- a/drivers/clk/clk-divider.c +++ b/drivers/clk/clk-divider.c @@ -159,8 +159,17 @@ static bool _is_valid_table_div(const struct clk_div_table *table, static bool _is_valid_div(const struct clk_div_table *table, unsigned int div, unsigned long flags) { - if (flags & CLK_DIVIDER_POWER_OF_TWO) - return is_power_of_2(div); + bool is_valid; + + if (flags & CLK_DIVIDER_POWER_OF_TWO) { + is_valid = is_power_of_2(div); + if (flags & CLK_DIVIDER_EVEN) + return is_valid && (div != 1); + return is_valid; + } + + if (flags & CLK_DIVIDER_EVEN) + return !(div % 2); if (table) return _is_valid_table_div(table, div); return true; @@ -208,6 +217,12 @@ static int _div_round_up(const struct clk_div_table *table, { int div = DIV_ROUND_UP_ULL((u64)parent_rate, rate); + /* + * Check even before power of two to avoid div 1 if combination + * happens, which applies to all the following similarities. + */ + if (flags & CLK_DIVIDER_EVEN) + div = !(div % 2) ? div : (div + 1); if (flags & CLK_DIVIDER_POWER_OF_TWO) div = __roundup_pow_of_two(div); if (table) @@ -226,6 +241,11 @@ static int _div_round_closest(const struct clk_div_table *table, up = DIV_ROUND_UP_ULL((u64)parent_rate, rate); down = parent_rate / rate; + if (flags & CLK_DIVIDER_EVEN) { + up = !(up % 2) ? up : (up + 1); + down = !(down % 2) ? down : (down - 1); + } + if (flags & CLK_DIVIDER_POWER_OF_TWO) { up = __roundup_pow_of_two(up); down = __rounddown_pow_of_two(down); @@ -264,6 +284,8 @@ static int _next_div(const struct clk_div_table *table, int div, { div++; + if (flags & CLK_DIVIDER_EVEN) + div = !(div % 2) ? div : (div + 1); if (flags & CLK_DIVIDER_POWER_OF_TWO) return __roundup_pow_of_two(div); if (table) diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h index 210a890..7c59611 100644 --- a/include/linux/clk-provider.h +++ b/include/linux/clk-provider.h @@ -388,6 +388,8 @@ struct clk_div_table { * CLK_DIVIDER_MAX_AT_ZERO - For dividers which are like CLK_DIVIDER_ONE_BASED * except when the value read from the register is zero, the divisor is * 2^width of the field. + * CLK_DIVIDER_EVEN - For the dividers which could only use even number in the + * div field. */ struct clk_divider { struct clk_hw hw; @@ -409,6 +411,7 @@ struct clk_divider { #define CLK_DIVIDER_ROUND_CLOSEST BIT(4) #define CLK_DIVIDER_READ_ONLY BIT(5) #define CLK_DIVIDER_MAX_AT_ZERO BIT(6) +#define CLK_DIVIDER_EVEN BIT(7) extern const struct clk_ops clk_divider_ops; extern const struct clk_ops clk_divider_ro_ops;
CLK_DIVIDER_EVEN is used for clock divders that should only use even number in the div field. Two clock divder should consider to use this flag (1) The divder is physically only support even div number to generate 50% duty cycle clock rate. (2) The divder's clock consumer request it to use even div number to generate the most closest requested rate for whatever reason. In some platforms, for instance Rockchip, the eMMC/SDIO/SDMMC should request divder to use even number when working at a high throughput speed mode reliably. However, that wasn't guaranteed by clock framework. So the previous tricky is to carefully assign magic clock rate to their parents as well as consumer's clock rate when requesting. That works bad in practice if folks change the parents clock rate or the clock hierarchy randomly. That also work bad if the consumer's clock rate came from the DT, which is changed so fraquent for different boards. To make it's less prone to make mistake and to make it really respect the fact that the divder should use even number to the div field, we need the clock framework's help. Now we have CLK_DIVIDER_POWER_OF_TWO, which could guarantee the div field is even number, however, obviously it skips the even numbers which isn't the power of 2, but maybe which is the best div to generate closest clock rate for consumer. Look at the examples here when doing some random test on Rockchip's platforms, by changing the requested clock rate from DT, namely assigning different max-frquency for MMC node, when the mmc host driver requests 80MHz with CLK_DIVIDER_POWER_OF_TWO flag for the clock divder, it shows the final clock rate is 61.44Mhz pll_vpll0 1 1 983039999 0 0 vpll0 4 4 983039999 0 0 clk_emmc_div 1 1 122880000 0 0 clk_emmc 1 1 122880000 0 0 emmc_sample 0 0 61440000 0 155 emmc_drv 0 0 61440000 0 180 With this patch and add CLK_DIVIDER_EVEN flag for clk_emmc_div, we get the final clock rate, 67.7376MHz. pll_vpll1 1 1 812851199 0 0 vpll1 2 2 812851199 0 0 clk_emmc_div 1 1 135475200 0 0 clk_emmc 1 1 135475200 0 0 emmc_sample 0 0 67737600 0 113 emmc_drv 0 0 67737600 0 180 Apprently 67737600 is better than 61440000 when requesting 80MHz. Of course, we could have more case that worsen the gap between the desired rate and the actual rate if using CLK_DIVIDER_POWER_OF_TWO. Alternatively, clk_div_table could be resorted to handle different kinds of div limilation, and it seems to be applied to irregular div calculation in practice by current clock provider drivers, but even number for div field is a rather common, regular and symmetrical requirement. So it is worth to introduces CLK_DIVIDER_EVEN flag for clock framework to make the best in this process. Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com> --- Changes in v3: - Fix a wrong if condition check Changes in v2: - Avoid to use div 1 if (CLK_DIVIDER_EVEN | CLK_DIVIDER_POWER_OF_TWO) suggested by Heiko. And seems actually no other flags should be bothered by this newly added CLK_DIVIDER_EVEN. drivers/clk/clk-divider.c | 26 ++++++++++++++++++++++++-- include/linux/clk-provider.h | 3 +++ 2 files changed, 27 insertions(+), 2 deletions(-)