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

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Date:	Thu, 14 Jan 2016 15:01:05 +0100
From:	Thierry Reding <thierry.reding@...il.com>
To:	Jon Hunter <jonathanh@...dia.com>
Cc:	Philipp Zabel <p.zabel@...gutronix.de>,
	Stephen Warren <swarren@...dotorg.org>,
	Alexandre Courbot <gnurou@...il.com>,
	Rafael Wysocki <rjw@...ysocki.net>,
	Kevin Hilman <khilman@...nel.org>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Vince Hsu <vinceh@...dia.com>, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: Re: [PATCH V4 06/16] soc: tegra: pmc: Wait for powergate state to
 change

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@...dia.com>
> ---
>  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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