Re: [PATCH v3] watchdog: renesas_wdt: Add a few cycles delay

[Guenter Roeck <linux@xxxxxxxxxxxx>]

[Note: I updated the subject to "PATCH v3"]

On Wed, Jun 05, 2019 at 02:04:00PM +0900, Yoshihiro Shimoda wrote:
> According to the hardware manual of R-Car Gen2 and Gen3,
> software should wait a few RLCK cycles as following:
>  - Delay 2 cycles before setting watchdog counter.
>  - Delay 3 cycles before disabling module clock.
> 
> So, this patch adds such delays.
> 
> Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
> Reviewed-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
> Reviewed-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>
> Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@xxxxxxxxxxxx>

Reviewed-by: Guenter Roeck <linux@xxxxxxxxxxxx>

> ---
>  Changes from v2 (https://patchwork.kernel.org/patch/10972721/):
>  - Rename the wait function name.
>  - Rename the variable name in the wait function.
>  - Change variable type.
>  - Add Wolfram-san and Niklas-san's Reviewed-by.
> 
>  Changes from v1 (https://patchwork.kernel.org/patch/10972641/):
>  - Change formula to improve accuracy.
>  - Add Geert-san's Reviewed-by.
> 
>  drivers/watchdog/renesas_wdt.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/watchdog/renesas_wdt.c b/drivers/watchdog/renesas_wdt.c
> index 565dbc1..0cfc0e9 100644
> --- a/drivers/watchdog/renesas_wdt.c
> +++ b/drivers/watchdog/renesas_wdt.c
> @@ -7,6 +7,7 @@
>   */
>  #include <linux/bitops.h>
>  #include <linux/clk.h>
> +#include <linux/delay.h>
>  #include <linux/io.h>
>  #include <linux/kernel.h>
>  #include <linux/module.h>
> @@ -70,6 +71,15 @@ static int rwdt_init_timeout(struct watchdog_device *wdev)
>  	return 0;
>  }
>  
> +static void rwdt_wait_cycles(struct rwdt_priv *priv, unsigned int cycles)
> +{
> +	unsigned int delay;
> +
> +	delay = DIV_ROUND_UP(cycles * 1000000, priv->clk_rate);
> +
> +	usleep_range(delay, 2 * delay);
> +}
> +
>  static int rwdt_start(struct watchdog_device *wdev)
>  {
>  	struct rwdt_priv *priv = watchdog_get_drvdata(wdev);
> @@ -80,6 +90,8 @@ static int rwdt_start(struct watchdog_device *wdev)
>  	/* Stop the timer before we modify any register */
>  	val = readb_relaxed(priv->base + RWTCSRA) & ~RWTCSRA_TME;
>  	rwdt_write(priv, val, RWTCSRA);
> +	/* Delay 2 cycles before setting watchdog counter */
> +	rwdt_wait_cycles(priv, 2);
>  
>  	rwdt_init_timeout(wdev);
>  	rwdt_write(priv, priv->cks, RWTCSRA);
> @@ -98,6 +110,8 @@ static int rwdt_stop(struct watchdog_device *wdev)
>  	struct rwdt_priv *priv = watchdog_get_drvdata(wdev);
>  
>  	rwdt_write(priv, priv->cks, RWTCSRA);
> +	/* Delay 3 cycles before disabling module clock */
> +	rwdt_wait_cycles(priv, 3);
>  	pm_runtime_put(wdev->parent);
>  
>  	return 0;