[PATCH v2] watchdog: renesas_wdt: Add a few cycles delay

[PATCH v2] watchdog: renesas_wdt: Add a few cycles delay

[Yoshihiro Shimoda]

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@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
 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..525a1fe 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(struct rwdt_priv *priv, unsigned int cycles)
+{
+	unsigned long delays;
+
+	delays = DIV_ROUND_UP(cycles * 1000000, priv->clk_rate);
+
+	usleep_range(delays, 2 * delays);
+}
+
 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(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(priv, 3);
 	pm_runtime_put(wdev->parent);
 
 	return 0;
-- 
2.7.4

Re: [PATCH v2] watchdog: renesas_wdt: Add a few cycles delay

[Wolfram Sang]

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On Mon, Jun 03, 2019 at 07:36:01PM +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@renesas.com>
> Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>

Despite minor nits:

Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

> +static void rwdt_wait(struct rwdt_priv *priv, unsigned int cycles)

I'd think 'rwdt_wait_cycles' would be a more precise name for this
function.

> +	unsigned long delays;

Why not just 'delay'?

> +	/* Delay 3 cycles before disabling module clock */

I like the comments explaining why it is needed.


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Re: [PATCH v2] watchdog: renesas_wdt: Add a few cycles delay

[Niklas Söderlund]

Hi Shimoda-san,

Thanks for your work.

On 2019-06-03 19:36:01 +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@renesas.com>
> Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>

Small nit bellow, with or without that addressed.

Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>

> ---
>  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..525a1fe 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(struct rwdt_priv *priv, unsigned int cycles)
> +{
> +	unsigned long delays;

Could this be unsigned int? It would still fit for a cycles number 
around 2000 and this change use 2 and 3 cycles.

> +
> +	delays = DIV_ROUND_UP(cycles * 1000000, priv->clk_rate);
> +
> +	usleep_range(delays, 2 * delays);
> +}
> +
>  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(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(priv, 3);
>  	pm_runtime_put(wdev->parent);
>  
>  	return 0;
> -- 
> 2.7.4
> 

-- 
Regards,
Niklas Söderlund

RE: [PATCH v2] watchdog: renesas_wdt: Add a few cycles delay

[Yoshihiro Shimoda]

Hi Wolfram-san,

> From: Wolfram Sang, Sent: Monday, June 3, 2019 10:04 PM
> On Mon, Jun 03, 2019 at 07:36:01PM +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@renesas.com>
> > Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
> 
> Despite minor nits:
> 
> Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

Thank you for your review!

> > +static void rwdt_wait(struct rwdt_priv *priv, unsigned int cycles)
> 
> I'd think 'rwdt_wait_cycles' would be a more precise name for this
> function.
> 
> > +	unsigned long delays;
> 
> Why not just 'delay'?

Ah, in v1, periods value existed. So, for consistence, I named "delay".
But, I think we should just "delay" in this case. I'll fix it.

> > +	/* Delay 3 cycles before disabling module clock */
> 
> I like the comments explaining why it is needed.

I think so!

Best regards,
Yoshihiro Shimoda

RE: [PATCH v2] watchdog: renesas_wdt: Add a few cycles delay

[Yoshihiro Shimoda]

Hi Niklas-san,

> From: Niklas Söderlund, Sent: Tuesday, June 4, 2019 1:23 AM
> 
> Hi Shimoda-san,
> 
> Thanks for your work.
> 
> On 2019-06-03 19:36:01 +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@renesas.com>
> > Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
> 
> Small nit bellow, with or without that addressed.
> 
> Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>

Thank you for your review!

<snip>
> > +static void rwdt_wait(struct rwdt_priv *priv, unsigned int cycles)
> > +{
> > +	unsigned long delays;
> 
> Could this be unsigned int? It would still fit for a cycles number
> around 2000 and this change use 2 and 3 cycles.

I think so. I'll fix it on v3.

Best regards,
Yoshihiro Shimoda