linux-kernel - Re: [PATCH v4 16/27] drm/panel: panel-simple: Get rid of hacky HPD chicken-and-egg code

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Message-ID: <YILex5oaMUQy5zs/@builder.lan>
Date:   Fri, 23 Apr 2021 09:50:47 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Sam Ravnborg <sam@...nborg.org>, Wolfram Sang <wsa@...nel.org>,
        Stephen Boyd <swboyd@...omium.org>, robdclark@...omium.org,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Stanislav Lisovskiy <stanislav.lisovskiy@...el.com>,
        Steev Klimaszewski <steev@...i.org>,
        linux-arm-msm@...r.kernel.org, Linus W <linus.walleij@...aro.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Thierry Reding <thierry.reding@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 16/27] drm/panel: panel-simple: Get rid of hacky HPD
 chicken-and-egg code

On Fri 16 Apr 17:39 CDT 2021, Douglas Anderson wrote:

> When I added support for the hpd-gpio to simple-panel in commit
> 48834e6084f1 ("drm/panel-simple: Support hpd-gpios for delaying
> prepare()"), I added a special case to handle a circular dependency I
> was running into on the ti-sn65dsi86 bridge chip. On my board the
> hpd-gpio is actually provided by the bridge chip. That was causing
> some circular dependency problems that I had to work around by getting
> the hpd-gpio late.
> 
> I've now reorganized the ti-sn65dsi86 bridge chip driver to be a
> collection of sub-drivers. Now the GPIO part can probe separately and
> that breaks the chain. Let's get rid of the old code to clean things
> up.
> 

Reviewed-by: Bjorn Andersson <bjorn.andersson@...aro.org>

Regards,
Bjorn

> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
> 
> (no changes since v1)
> 
>  drivers/gpu/drm/panel/panel-simple.c | 24 +++++-------------------
>  1 file changed, 5 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
> index 6b22872b3281..90a17ca79d06 100644
> --- a/drivers/gpu/drm/panel/panel-simple.c
> +++ b/drivers/gpu/drm/panel/panel-simple.c
> @@ -366,8 +366,7 @@ static int panel_simple_unprepare(struct drm_panel *panel)
>  	return 0;
>  }
>  
> -static int panel_simple_get_hpd_gpio(struct device *dev,
> -				     struct panel_simple *p, bool from_probe)
> +static int panel_simple_get_hpd_gpio(struct device *dev, struct panel_simple *p)
>  {
>  	int err;
>  
> @@ -375,17 +374,10 @@ static int panel_simple_get_hpd_gpio(struct device *dev,
>  	if (IS_ERR(p->hpd_gpio)) {
>  		err = PTR_ERR(p->hpd_gpio);
>  
> -		/*
> -		 * If we're called from probe we won't consider '-EPROBE_DEFER'
> -		 * to be an error--we'll leave the error code in "hpd_gpio".
> -		 * When we try to use it we'll try again.  This allows for
> -		 * circular dependencies where the component providing the
> -		 * hpd gpio needs the panel to init before probing.
> -		 */
> -		if (err != -EPROBE_DEFER || !from_probe) {
> +		if (err != -EPROBE_DEFER)
>  			dev_err(dev, "failed to get 'hpd' GPIO: %d\n", err);
> -			return err;
> -		}
> +
> +		return err;
>  	}
>  
>  	return 0;
> @@ -416,12 +408,6 @@ static int panel_simple_prepare_once(struct panel_simple *p)
>  		msleep(delay);
>  
>  	if (p->hpd_gpio) {
> -		if (IS_ERR(p->hpd_gpio)) {
> -			err = panel_simple_get_hpd_gpio(dev, p, false);
> -			if (err)
> -				goto error;
> -		}
> -
>  		if (p->desc->delay.hpd_absent_delay)
>  			hpd_wait_us = p->desc->delay.hpd_absent_delay * 1000UL;
>  		else
> @@ -682,7 +668,7 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc)
>  
>  	panel->no_hpd = of_property_read_bool(dev->of_node, "no-hpd");
>  	if (!panel->no_hpd) {
> -		err = panel_simple_get_hpd_gpio(dev, panel, true);
> +		err = panel_simple_get_hpd_gpio(dev, panel);
>  		if (err)
>  			return err;
>  	}
> -- 
> 2.31.1.368.gbe11c130af-goog
>