Re: [PATCH V5 05/14] soc: tegra: pmc: Wait for powergate state to change

[Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>]

On 29/01/16 16:58, Mathieu Poirier wrote:
> On 28 January 2016 at 09:33, Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org> wrote:
>> Currently, the function tegra_powergate_set() simply sets the desired
>> powergate state but does not wait for the state to change. In most cases
>> we should wait for the state to change before proceeding. Currently, there
>> is a case for tegra114 and tegra124 devices where we do not wait when
>> starting the secondary CPU as this is not necessary. However, this is only
>> done at boot time and so waiting here will only have a small impact on
>> boot time. Therefore, update tegra_powergate_set() to wait when setting
>> the powergate.
>>
>> By adding this feature, we can also eliminate the polling loop from
>> tegra30_boot_secondary().
>>
>> A function has been added for checking the status of the powergate and
>> so update the tegra_powergate_is_powered() to use this macro as well.
>>
>> Signed-off-by: Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
>> ---
>>  arch/arm/mach-tegra/platsmp.c | 16 +++-------------
>>  drivers/soc/tegra/pmc.c       |  9 ++++++++-
>>  2 files changed, 11 insertions(+), 14 deletions(-)
>>
>> diff --git a/arch/arm/mach-tegra/platsmp.c b/arch/arm/mach-tegra/platsmp.c
>> index f3f61dbbda97..75620ae73913 100644
>> --- a/arch/arm/mach-tegra/platsmp.c
>> +++ b/arch/arm/mach-tegra/platsmp.c
>> @@ -108,19 +108,9 @@ static int tegra30_boot_secondary(unsigned int cpu, struct task_struct *idle)
>>          * be un-gated by un-toggling the power gate register
>>          * manually.
>>          */
>> -       if (!tegra_pmc_cpu_is_powered(cpu)) {
>> -               ret = tegra_pmc_cpu_power_on(cpu);
>> -               if (ret)
>> -                       return ret;
>> -
>> -               /* Wait for the power to come up. */
>> -               timeout = jiffies + msecs_to_jiffies(100);
>> -               while (!tegra_pmc_cpu_is_powered(cpu)) {
>> -                       if (time_after(jiffies, timeout))
>> -                               return -ETIMEDOUT;
>> -                       udelay(10);
>> -               }
>> -       }
>> +       ret = tegra_pmc_cpu_power_on(cpu);
>> +       if (ret)
>> +               return ret;
>>
>>  remove_clamps:
>>         /* CPU partition is powered. Enable the CPU clock. */
>> diff --git a/drivers/soc/tegra/pmc.c b/drivers/soc/tegra/pmc.c
>> index 99cb2fdd29e1..35ee60fd17be 100644
>> --- a/drivers/soc/tegra/pmc.c
>> +++ b/drivers/soc/tegra/pmc.c
>> @@ -28,6 +28,7 @@
>>  #include <linux/export.h>
>>  #include <linux/init.h>
>>  #include <linux/io.h>
>> +#include <linux/iopoll.h>
>>  #include <linux/of.h>
>>  #include <linux/of_address.h>
>>  #include <linux/platform_device.h>
>> @@ -186,6 +187,9 @@ static inline bool tegra_powergate_state(int id)
>>   */
>>  static int tegra_powergate_set(unsigned int id, bool new_state)
>>  {
>> +       bool status;
>> +       int err;
>> +
>>         mutex_lock(&pmc->powergates_lock);
>>
>>         if (tegra_powergate_state(id) == new_state) {
>> @@ -195,9 +199,12 @@ static int tegra_powergate_set(unsigned int id, bool new_state)
>>
>>         tegra_pmc_writel(PWRGATE_TOGGLE_START | id, PWRGATE_TOGGLE);
>>
>> +       err = readx_poll_timeout(tegra_powergate_state, id, status,
>> +                                status == new_state, 10, 100000);
>> +
> 
> I understand (and agree) with the goal of this patch but I wonder (and
> I don't know much about the system/context) if holding a mutex while
> sleeping won't incur adverse effect on other parts of the system that
> weren't use to see this wait.  One way to fix this might be to use
> "mutex_trylock()" and let callers retry as they see fit if an
> operation is already in progress.

I could unlock the mutex after writing the TOGGLE_START register. I
don't believe that we need to waiting for a powergate to change before
writing again.

Jon