From: Stephen Boyd <swboyd@chromium.org>
To: Douglas Anderson <dianders@chromium.org>,
Laurent.pinchart@ideasonboard.com, a.hajda@samsung.com,
airlied@linux.ie, bgolaszewski@baylibre.com, daniel@ffwll.ch,
linus.walleij@linaro.org, narmstrong@baylibre.com,
robh+dt@kernel.org, spanda@codeaurora.org
Cc: jonas@kwiboo.se, jeffrey.l.hugo@gmail.com,
linux-gpio@vger.kernel.org, linux-arm-msm@vger.kernel.org,
dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org,
jernej.skrabec@siol.net, bjorn.andersson@linaro.org,
robdclark@chromium.org, Douglas Anderson <dianders@chromium.org>,
Sam Ravnborg <sam@ravnborg.org>,
Thierry Reding <thierry.reding@gmail.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 3/6] drm/panel-simple: Support hpd-gpios for delaying prepare()
Date: Wed, 22 Apr 2020 14:12:20 -0700 [thread overview]
Message-ID: <158758994028.230545.10042873479857418029@swboyd.mtv.corp.google.com> (raw)
In-Reply-To: <20200420220458.v2.3.I53fed5b501a31e7a7fa13268ebcdd6b77bd0cadd@changeid>
Quoting Douglas Anderson (2020-04-20 22:06:19)
> People use panel-simple when they have panels that are builtin to
> their device. In these cases the HPD (Hot Plug Detect) signal isn't
> really used for hotplugging devices but instead is used for power
> sequencing. Panel timing diagrams (especially for eDP panels) usually
> have the HPD signal in them and it acts as an indicator that the panel
> is ready for us to talk to it.
>
> Sometimes the HPD signal is hooked up to a normal GPIO on a system.
> In this case we need to poll it in the correct place to know that the
> panel is ready for us. In some system designs the right place for
> this is panel-simple.
>
> When adding this support, we'll account for the case that there might
> be a circular dependency between panel-simple and the provider of the
> GPIO. The case this was designed for was for the "ti-sn65dsi86"
> bridge chip. If HPD is hooked up to one of the GPIOs provided by the
> bridge chip then in our probe function we'll always get back
> -EPROBE_DEFER. Let's handle this by allowing this GPIO to show up
> late if we saw -EPROBE_DEFER during probe.
May be worth mentioning that if there isn't an hpd-gpios property then
we only try once during probe and then after that the prepare callback
doesn't try again because the gpio_get_optional() APIs are used. I had
to think about that for a minute.
>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
next prev parent reply other threads:[~2020-04-22 21:12 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-21 5:06 [PATCH v2 0/6] drm: Prepare to use a GPIO on ti-sn65dsi86 for Hot Plug Detect Douglas Anderson
2020-04-21 5:06 ` [PATCH v2 1/6] drm/bridge: ti-sn65dsi86: Export bridge GPIOs to Linux Douglas Anderson
2020-04-22 10:23 ` Stephen Boyd
2020-04-22 16:09 ` Doug Anderson
2020-04-21 5:06 ` [PATCH v2 2/6] dt-bindings: display: Add hpd-gpios to panel-common bindings Douglas Anderson
2020-04-22 10:24 ` Stephen Boyd
2020-04-21 5:06 ` [PATCH v2 3/6] drm/panel-simple: Support hpd-gpios for delaying prepare() Douglas Anderson
2020-04-22 21:12 ` Stephen Boyd [this message]
2020-04-21 5:06 ` [PATCH v2 4/6] dt-bindings: drm/bridge: ti-sn65dsi86: Convert to yaml Douglas Anderson
2020-04-21 5:06 ` [PATCH v2 5/6] dt-bindings: drm/bridge: ti-sn65dsi86: Document no-hpd Douglas Anderson
2020-04-22 10:26 ` Stephen Boyd
2020-04-21 5:06 ` [PATCH v2 6/6] arm64: dts: sdm845: Add "no-hpd" to sn65dsi86 on cheza Douglas Anderson
2020-04-22 10:26 ` Stephen Boyd
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