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[209.85.210.173]) by smtp.gmail.com with ESMTPSA id c10sm8857078pfm.50.2020.05.18.07.50.43 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 18 May 2020 07:50:45 -0700 (PDT) Received: by mail-pf1-f173.google.com with SMTP id n15so1832170pfd.0 for ; Mon, 18 May 2020 07:50:43 -0700 (PDT) X-Received: by 2002:a67:e884:: with SMTP id x4mr7166181vsn.106.1589813441464; Mon, 18 May 2020 07:50:41 -0700 (PDT) MIME-Version: 1.0 References: <20200507213500.241695-1-dianders@chromium.org> <20200509201511.GD30802@ravnborg.org> In-Reply-To: From: Doug Anderson Date: Mon, 18 May 2020 07:50:29 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v5 0/6] drm: Prepare to use a GPIO on ti-sn65dsi86 for Hot Plug Detect To: Sam Ravnborg , LinusW , Stephen Boyd , Laurent Pinchart Cc: Bartosz Golaszewski , David Airlie , Daniel Vetter , Rob Herring , Neil Armstrong , Andrzej Hajda , Sandeep Panda , Rob Clark , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , Jernej Skrabec , Jeffrey Hugo , Stephen Boyd , linux-arm-msm , Jonas Karlman , dri-devel , "open list:GPIO SUBSYSTEM" , Andy Gross , Thierry Reding , Krzysztof Kozlowski , Paul Walmsley , Bjorn Andersson , LKML Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Sam, On Sat, May 9, 2020 at 3:48 PM Doug Anderson wrote: > > Hi, > > On Sat, May 9, 2020 at 1:15 PM Sam Ravnborg wrote: > > > > Hi Douglas. > > > > On Thu, May 07, 2020 at 02:34:54PM -0700, Douglas Anderson wrote: > > > > > > As talked about in commit c2bfc223882d ("drm/bridge: ti-sn65dsi86: > > > Remove the mystery delay"), the normal HPD pin on ti-sn65dsi86 is > > > kinda useless, at least for embedded DisplayPort (eDP). However, > > > despite the fact that the actual HPD pin on the bridge is mostly > > > useless for eDP, the concept of HPD for eDP still makes sense. It > > > allows us to optimize out a hardcoded delay that many panels need if > > > HPD isn't hooked up. Panel timing diagrams show HPD as one of the > > > events to measure timing from and we have to assume the worst case if > > > we can't actually read HPD. > > > > > > One way to use HPD for eDP without using the mostly useless HPD pin on > > > ti-sn65dsi86 is to route the panel's HPD somewhere else in the system, > > > like to a GPIO. This works great because eDP panels aren't physically > > > hotplugged. That means the debouncing logic that caused us problems > > > wasn't really needed and a raw GPIO works great. > > > > > > As per the above, a smart board designer would realize the value of > > > HPD and choose to route it to a GPIO somewhere on the board to avoid > > > the silly sn65dsi86 debouncing. While said "smart designer" could > > > theoretically route HPD anywhere on the board, a really smart designer > > > would realize that there are several GPIOs on the bridge itself that > > > are nearly useless for anything but this purpose and route HPD to one > > > of those. > > > > > > This series of patches is intended to allow the scenario described > > > above. > > > > > > This patch has been tested on a board that is not yet mainline. On > > > the hardware I have: > > > - Panel spec says HPD could take up to 200 ms to come up, so without > > > HPD hooked up we need to delay 200 ms. > > > - On my board the panel is powered by the same rail as the > > > touchscreen. By chance of probe order the touchscreen comes up > > > first. This means by the time we check HPD in ti_sn_bridge_enable() > > > it's already up. Thus we can use the panel on 200 ms earlier. > > > - If I measure HPD on this pane it comes up ~56 ms after the panel is > > > powered. This means I can save 144 ms of delay. > > > > > > Side effects (though not main goals) of this series are: > > > - ti-sn65dsi86 GPIOs are now exported in Linux. > > > - ti-sn65dsi86 bindings are converted to yaml. > > > - Common panel bindings now have "hpd-gpios" listed. > > > - The simple-panel driver in Linux can delay in prepare based on > > > "hpd-gpios" > > > - ti-sn65dsi86 bindings (and current user) now specifies "no-hpd" > > > if HPD isn't hooked up. > > > > > > Changes in v5: > > > - Use of_xlate so that numbers in dts start at 1, not 0. > > > - Squash https://lore.kernel.org/r/20200506140208.v2.2.I0a2bca02b09c1fcb6b09479b489736d600b3e57f@changeid/ > > > > > > Changes in v4: > > > - Don't include gpio.h > > > - Use gpiochip_get_data() instead of container_of() to get data. > > > - GPIOF_DIR_XXX => GPIO_LINE_DIRECTION_XXX > > > - Use Linus W's favorite syntax to read a bit from a bitfield. > > > - Define and use SN_GPIO_MUX_MASK. > > > - Add a comment about why we use a bitmap for gchip_output. > > > - Tacked on "or is otherwise unusable." to description. > > > > > > Changes in v3: > > > - Becaue => Because > > > - Add a kernel-doc to our pdata to clarify double-duty of gchip_output. > > > - More comments about how powering off affects us (get_dir, dir_input). > > > - Cleanup tail of ti_sn_setup_gpio_controller() to avoid one "return". > > > - Use a bitmap rather than rolling my own. > > > - Remind how gpio_get_optional() works in the commit message. > > > - useful implement => useful to implement > > > > > > Changes in v2: > > > - ("Export...GPIOs") is 1/2 of replacement for ("Allow...bridge GPIOs") > > > - ("dt-bindings: display: Add hpd-gpios to panel-common...") new for v2 > > > - ("simple...hpd-gpios") is 1/2 of replacement for ("Allow...bridge GPIOs") > > > - specification => specifier. > > > - power up => power. > > > - Added back missing suspend-gpios. > > > - data-lanes and lane-polarities are are the right place now. > > > - endpoints don't need to be patternProperties. > > > - Specified more details for data-lanes and lane-polarities. > > > - Added old example back in, fixing bugs in it. > > > - Example i2c bus is just called "i2c", not "i2c1" now. > > > - ("dt-bindings: drm/bridge: ti-sn65dsi86: Document no-hpd") new for v2. > > > - ("arm64: dts: sdm845: Add "no-hpd" to sn65dsi86 on cheza") new for v2. > > > > > > Douglas Anderson (6): > > > drm/bridge: ti-sn65dsi86: Export bridge GPIOs to Linux > > > dt-bindings: display: Add hpd-gpios to panel-common bindings > > > drm/panel-simple: Support hpd-gpios for delaying prepare() > > > dt-bindings: drm/bridge: ti-sn65dsi86: Convert to yaml > > > dt-bindings: drm/bridge: ti-sn65dsi86: Document no-hpd > > > arm64: dts: sdm845: Add "no-hpd" to sn65dsi86 on cheza > > > > Applied: > > > dt-bindings: display: Add hpd-gpios to panel-common bindings > > > drm/panel-simple: Support hpd-gpios for delaying prepare() > > to drm-misc-next. > > > > The others was missing reviews so we need to wait for feedback. > > Thanks! > > Given the previous feedback from Linus W, Stephen, and Laurent I > expect things are good enough to land now, but it'd be good to get > confirmation (I removed some of the previous tags just to get > confirmation). If we can get review tags early next week maybe it'll > still be in time to land for 5.8? I think all the others have reviews now. Is there anything blocking them from getting applied? Thanks! -Doug