linux-kernel - Re: [PATCH 5/9] drm/bridge: tc358767: Simplify polling in tc_link

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Date:   Mon, 4 Mar 2019 14:30:52 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Andrey Smirnov <andrew.smirnov@...il.com>
Cc:     dri-devel@...ts.freedesktop.org,
        Archit Taneja <architt@...eaurora.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Chris Healy <cphealy@...il.com>,
        Lucas Stach <l.stach@...gutronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/9] drm/bridge: tc358767: Simplify polling in
 tc_link_training()

Hi Andrey,

Thank you for the patch.

On Tue, Feb 26, 2019 at 11:36:05AM -0800, Andrey Smirnov wrote:
> Replace explicit polling in tc_link_training() with equivalent call to
> regmap_read_poll_timeout() for simplicity. No functional change
> intended (not including slightly altered debug output).
> 
> Signed-off-by: Andrey Smirnov <andrew.smirnov@...il.com>
> Cc: Archit Taneja <architt@...eaurora.org>
> Cc: Andrzej Hajda <a.hajda@...sung.com>
> Cc: Laurent Pinchart <Laurent.pinchart@...asonboard.com>
> Cc: Chris Healy <cphealy@...il.com>
> Cc: Lucas Stach <l.stach@...gutronix.de>
> Cc: dri-devel@...ts.freedesktop.org
> Cc: linux-kernel@...r.kernel.org
> ---
>  drivers/gpu/drm/bridge/tc358767.c | 14 +++++---------
>  1 file changed, 5 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/tc358767.c b/drivers/gpu/drm/bridge/tc358767.c
> index 6455e6484722..ea30cec4a0c3 100644
> --- a/drivers/gpu/drm/bridge/tc358767.c
> +++ b/drivers/gpu/drm/bridge/tc358767.c
> @@ -735,7 +735,6 @@ static int tc_link_training(struct tc_data *tc, int pattern)
>  	const char * const *errors;
>  	u32 srcctrl = tc_srcctrl(tc) | DP0_SRCCTRL_SCRMBLDIS |
>  		      DP0_SRCCTRL_AUTOCORRECT;
> -	int timeout;
>  	int retry;
>  	u32 value;
>  	int ret;
> @@ -765,20 +764,17 @@ static int tc_link_training(struct tc_data *tc, int pattern)
>  		tc_write(DP0CTL, DP_EN);
>  
>  		/* wait */
> -		timeout = 1000;
> -		do {
> -			tc_read(DP0_LTSTAT, &value);
> -			udelay(1);
> -		} while ((!(value & LT_LOOPDONE)) && (--timeout));
> -		if (timeout == 0) {
> +		ret = regmap_read_poll_timeout(tc->regmap, DP0_LTSTAT, value,
> +					       value & LT_LOOPDONE, 1, 1000);
> +		if (ret) {
>  			dev_err(tc->dev, "Link training timeout!\n");
>  		} else {
>  			int pattern = (value >> 11) & 0x3;
>  			int error = (value >> 8) & 0x7;
>  
>  			dev_dbg(tc->dev,
> -				"Link training phase %d done after %d uS: %s\n",
> -				pattern, 1000 - timeout, errors[error]);
> +				"Link training phase %d done: %s\n",
> +				pattern, errors[error]);

It's probably not a big deal in this specific case, but in general it
can be useful to know how long the poll took. Any hope to enhance
regmap_read_poll_timeout() to return either the elapsed time or the
remaining timeout instead of 0 on success ?

>  			if (pattern == DP_TRAINING_PATTERN_1 && error == 0)
>  				break;
>  			if (pattern == DP_TRAINING_PATTERN_2) {

-- 
Regards,

Laurent Pinchart