Re: [PATCH V4 06/16] soc: tegra: pmc: Wait for powergate state to change

Thierry Reding
2016-01-14T14:01:05Z

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On Fri, Dec 04, 2015 at 02:57:07PM +0000, Jon Hunter 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 macro has also been adding for checking the status of the powergate and

"added"

> 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 | 21 +++++++++++++++------
> 2 files changed, 18 insertions(+), 19 deletions(-)
>
> diff --git a/arch/arm/mach-tegra/platsmp.c b/arch/arm/mach-tegra/platsmp.c
> index b45086666648..40cb761e7c95 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. */

I vaguely remember this being very brittle. I assume you've tested this
extensively and made sure it doesn't regress?

> diff --git a/drivers/soc/tegra/pmc.c b/drivers/soc/tegra/pmc.c
> index fdd1a8d0940f..f94d970089ce 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>
> @@ -101,6 +102,8 @@
>
> #define GPU_RG_CNTRL 0x2d4
>
> +#define PMC_PWRGATE_STATE(status, id) ((status & BIT(id)) != 0)
> +

This looks suspiciously like a register or register field definition.
Maybe turn this into a static inline function, such as:

static inline bool tegra_powergate_state(u32 status, int id)
{
return (status & BIT(id)) != 0;
}

?

> struct tegra_pmc_soc {
> unsigned int num_powergates;
> const char *const *powergates;
> @@ -181,22 +184,27 @@ static void tegra_pmc_writel(u32 value, unsigned long offset)
> */
> static int tegra_powergate_set(int id, bool new_state)
> {
> - bool status;
> + u32 status;
> + int err = 0;

Initialization to 0 doesn't seem necessary here.

Thierry

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