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Clocks used by another OS/CPU

Message ID 50911172-8fa1-8341-0ed0-d40f00d9392c@de.bosch.com (mailing list archive)
State RFC
Headers show

Commit Message

Dirk Behme June 29, 2017, 12:07 p.m. UTC 
On 29.06.2017 13:56, Geert Uytterhoeven wrote:
> Hi Dirk,
> 
> On Thu, Jun 29, 2017 at 11:27 AM, Geert Uytterhoeven
> <geert@linux-m68k.org> wrote:
>> CC clock, ARM, DT, PM people
>>
>> TL;DR: Clocks may be in use by another CPU not running Linux, while Linux
>> disables them as being unused.
> 
>> Of course this is not limited to clocks, but also to e.g. PM domains.
> 
> BTW, how do you prevent Linux from powering down the CR7 PM domain,
> which contains the Cortex R7?


The idea is

  	{ "a2vc1",	0x3c0, 1, R8A7795_PD_A2VC1,	R8A7795_PD_A3VC },


Not finally tested, though.

Best regards

Dirk
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Comments

Geert Uytterhoeven June 29, 2017, 12:45 p.m. UTC | #1 
Hi Dirk,

On Thu, Jun 29, 2017 at 2:07 PM, Dirk Behme <dirk.behme@de.bosch.com> wrote:
> On 29.06.2017 13:56, Geert Uytterhoeven wrote:
>> On Thu, Jun 29, 2017 at 11:27 AM, Geert Uytterhoeven
>> <geert@linux-m68k.org> wrote:
>>> CC clock, ARM, DT, PM people
>>>
>>> TL;DR: Clocks may be in use by another CPU not running Linux, while Linux
>>> disables them as being unused.
>>
>>> Of course this is not limited to clocks, but also to e.g. PM domains.
>>
>> BTW, how do you prevent Linux from powering down the CR7 PM domain,
>> which contains the Cortex R7?
>
> The idea is
>
> --- a/drivers/soc/renesas/r8a7795-sysc.c
> +++ b/drivers/soc/renesas/r8a7795-sysc.c
> @@ -38,7 +38,8 @@ static const struct rcar_sysc_area r8a7795_areas[]
> __initconst = {
>         { "ca53-cpu3",  0x200, 3, R8A7795_PD_CA53_CPU3, R8A7795_PD_CA53_SCU,
>           PD_CPU_NOCR },
>         { "a3vp",       0x340, 0, R8A7795_PD_A3VP,      R8A7795_PD_ALWAYS_ON
> },
> -       { "cr7",        0x240, 0, R8A7795_PD_CR7,       R8A7795_PD_ALWAYS_ON
> },
> +       { "cr7",        0x240, 0, R8A7795_PD_CR7,
> R8A7795_PD_ALWAYS_ON,
> +         PD_CPU_NOCR },
>         { "a3vc",       0x380, 0, R8A7795_PD_A3VC,      R8A7795_PD_ALWAYS_ON
> },
>         { "a2vc0",      0x3c0, 0, R8A7795_PD_A2VC0,     R8A7795_PD_A3VC },
>         { "a2vc1",      0x3c0, 1, R8A7795_PD_A2VC1,     R8A7795_PD_A3VC },
>
>
> Not finally tested, though.

Pretending the CR7 PM Domain can only be controlled through WFI/APMU only should
work.
But IMHO it is a hack, just like your solution for the CANFD clock.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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Dirk Behme June 29, 2017, 12:55 p.m. UTC | #2 
On 29.06.2017 14:45, Geert Uytterhoeven wrote:
> Hi Dirk,
> 
> On Thu, Jun 29, 2017 at 2:07 PM, Dirk Behme <dirk.behme@de.bosch.com> wrote:
>> On 29.06.2017 13:56, Geert Uytterhoeven wrote:
>>> On Thu, Jun 29, 2017 at 11:27 AM, Geert Uytterhoeven
>>> <geert@linux-m68k.org> wrote:
>>>> CC clock, ARM, DT, PM people
>>>>
>>>> TL;DR: Clocks may be in use by another CPU not running Linux, while Linux
>>>> disables them as being unused.
>>>
>>>> Of course this is not limited to clocks, but also to e.g. PM domains.
>>>
>>> BTW, how do you prevent Linux from powering down the CR7 PM domain,
>>> which contains the Cortex R7?
>>
>> The idea is
>>
>> --- a/drivers/soc/renesas/r8a7795-sysc.c
>> +++ b/drivers/soc/renesas/r8a7795-sysc.c
>> @@ -38,7 +38,8 @@ static const struct rcar_sysc_area r8a7795_areas[]
>> __initconst = {
>>          { "ca53-cpu3",  0x200, 3, R8A7795_PD_CA53_CPU3, R8A7795_PD_CA53_SCU,
>>            PD_CPU_NOCR },
>>          { "a3vp",       0x340, 0, R8A7795_PD_A3VP,      R8A7795_PD_ALWAYS_ON
>> },
>> -       { "cr7",        0x240, 0, R8A7795_PD_CR7,       R8A7795_PD_ALWAYS_ON
>> },
>> +       { "cr7",        0x240, 0, R8A7795_PD_CR7,
>> R8A7795_PD_ALWAYS_ON,
>> +         PD_CPU_NOCR },
>>          { "a3vc",       0x380, 0, R8A7795_PD_A3VC,      R8A7795_PD_ALWAYS_ON
>> },
>>          { "a2vc0",      0x3c0, 0, R8A7795_PD_A2VC0,     R8A7795_PD_A3VC },
>>          { "a2vc1",      0x3c0, 1, R8A7795_PD_A2VC1,     R8A7795_PD_A3VC },
>>
>>
>> Not finally tested, though.
> 
> Pretending the CR7 PM Domain can only be controlled through WFI/APMU only should
> work.
> But IMHO it is a hack, just like your solution for the CANFD clock.


Well, it seems to be the best solution recent mainline gives us and 
seems to work ;)

And for me it looks at least better than the other solution I've seen so 
far: Remove the 'cr7', 'canfd' etc lines completely from the kernel.

Best regards

Dirk
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diff mbox

Patch

--- a/drivers/soc/renesas/r8a7795-sysc.c
+++ b/drivers/soc/renesas/r8a7795-sysc.c
@@ -38,7 +38,8 @@  static const struct rcar_sysc_area r8a7795_areas[] 
__initconst = {
  	{ "ca53-cpu3",	0x200, 3, R8A7795_PD_CA53_CPU3,	R8A7795_PD_CA53_SCU,
  	  PD_CPU_NOCR },
  	{ "a3vp",	0x340, 0, R8A7795_PD_A3VP,	R8A7795_PD_ALWAYS_ON },
-	{ "cr7",	0x240, 0, R8A7795_PD_CR7,	R8A7795_PD_ALWAYS_ON },
+	{ "cr7",	0x240, 0, R8A7795_PD_CR7,	R8A7795_PD_ALWAYS_ON,
+	  PD_CPU_NOCR },
  	{ "a3vc",	0x380, 0, R8A7795_PD_A3VC,	R8A7795_PD_ALWAYS_ON },
  	{ "a2vc0",	0x3c0, 0, R8A7795_PD_A2VC0,	R8A7795_PD_A3VC },