From: Linus Walleij <linus.walleij@linaro.org>
To: Douglas Anderson <dianders@chromium.org>
Cc: Bartosz Golaszewski <bgolaszewski@baylibre.com>,
Dave Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
Rob Herring <robh+dt@kernel.org>,
Neil Armstrong <narmstrong@baylibre.com>,
Andrzej Hajda <a.hajda@samsung.com>,
Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
Sandeep Panda <spanda@codeaurora.org>,
Stephen Boyd <swboyd@chromium.org>,
"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
<devicetree@vger.kernel.org>,
"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
Jeffrey Hugo <jeffrey.l.hugo@gmail.com>,
"open list:DRM PANEL DRIVERS" <dri-devel@lists.freedesktop.org>,
MSM <linux-arm-msm@vger.kernel.org>,
Rob Clark <robdclark@chromium.org>,
Jernej Skrabec <jernej.skrabec@siol.net>,
Jonas Karlman <jonas@kwiboo.se>,
Bjorn Andersson <bjorn.andersson@linaro.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 5/6] dt-bindings: drm/bridge: ti-sn65dsi86: Document no-hpd
Date: Tue, 28 Apr 2020 14:25:42 +0200 [thread overview]
Message-ID: <CACRpkdZkRKgRo2-pxiyoz-3W_aoR+qb+AA-4+ZaPtt2Ykecs0w@mail.gmail.com> (raw)
In-Reply-To: <20200423092431.v3.5.I72892d485088e57378a4748c86bc0f6c2494d807@changeid>
On Thu, Apr 23, 2020 at 6:26 PM Douglas Anderson <dianders@chromium.org> wrote:
> The ti-sn65dsi86 MIPI DSI to eDP bridge chip has a dedicated hardware
> HPD (Hot Plug Detect) pin on it, but it's mostly useless for eDP
> because of excessive debouncing in hardware. Specifically there is no
> way to disable the debouncing and for eDP debouncing hurts you because
> HPD is just used for knowing when the panel is ready, not for
> detecting physical plug events.
>
> Currently the driver in Linux just assumes that nobody has HPD hooked
> up. It relies on folks setting the "no-hpd" property in the panel
> node to specify that HPD isn't hooked up and then the panel driver
> using this to add some worst case delays when turning on the panel.
>
> Apparently it's also useful to specify "no-hpd" in the bridge node so
> that the bridge driver can make sure it's doing the right thing
> without peeking into the panel [1]. This would be used if anyone ever
> found it useful to implement support for the HW HPD pin on the bridge.
> Let's add this property to the bindings.
>
> NOTES:
> - This is somewhat of a backward-incompatible change. All current
> known users of ti-sn65dsi86 didn't have "no-hpd" specified in the
> bridge node yet none of them had HPD hooked up. This worked because
> the current Linux driver just assumed that HPD was never hooked up.
> We could make it less incompatible by saying that for this bridge
> it's assumed HPD isn't hooked up _unless_ a property is defined, but
> "no-hpd" is much more standard and it's unlikely to matter unless
> someone quickly goes and implements HPD in the driver.
> - It is sensible to specify "no-hpd" at the bridge chip level and
> specify "hpd-gpios" at the panel level. That would mean HPD is
> hooked up to some other GPIO in the system, just not the hardware
> HPD pin on the bridge chip.
>
> [1] https://lore.kernel.org/r/20200417180819.GE5861@pendragon.ideasonboard.com
>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Makes sense to me so:
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
> + no-hpd:
> + type: boolean
> + description: Set if the HPD line on the bridge isn't hooked up to anything.
I would perhaps tag on:
... or is otherwise unusable?
Yours,
Linus Walleij
next prev parent reply other threads:[~2020-04-28 12:26 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-23 16:25 [PATCH v3 0/6] drm: Prepare to use a GPIO on ti-sn65dsi86 for Hot Plug Detect Douglas Anderson
2020-04-23 16:25 ` [PATCH v3 1/6] drm/bridge: ti-sn65dsi86: Export bridge GPIOs to Linux Douglas Anderson
2020-04-25 19:38 ` Stephen Boyd
2020-04-28 12:44 ` Linus Walleij
2020-04-29 0:45 ` Doug Anderson
2020-04-23 16:25 ` [PATCH v3 2/6] dt-bindings: display: Add hpd-gpios to panel-common bindings Douglas Anderson
2020-04-28 12:17 ` Linus Walleij
2020-04-23 16:25 ` [PATCH v3 3/6] drm/panel-simple: Support hpd-gpios for delaying prepare() Douglas Anderson
2020-04-28 12:21 ` Linus Walleij
2020-04-23 16:25 ` [PATCH v3 4/6] dt-bindings: drm/bridge: ti-sn65dsi86: Convert to yaml Douglas Anderson
2020-04-25 19:32 ` Stephen Boyd
2020-04-23 16:25 ` [PATCH v3 5/6] dt-bindings: drm/bridge: ti-sn65dsi86: Document no-hpd Douglas Anderson
2020-04-28 12:25 ` Linus Walleij [this message]
2020-04-23 16:25 ` [PATCH v3 6/6] arm64: dts: sdm845: Add "no-hpd" to sn65dsi86 on cheza Douglas Anderson
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