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[2001:14ba:a0db:1f00::8a5]) by smtp.gmail.com with ESMTPSA id 23-20020ac24837000000b005008286c06bsm1483944lft.91.2023.09.11.14.15.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 11 Sep 2023 14:15:11 -0700 (PDT) Message-ID: <6b6bacee-f7b6-4cfe-be3d-24bda44bfbcf@linaro.org> Date: Tue, 12 Sep 2023 00:15:10 +0300 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v1 01/12] Revert "drm/sysfs: Link DRM connectors to corresponding Type-C connectors" Content-Language: en-GB To: Heikki Krogerus Cc: David Airlie , Daniel Vetter , Andrzej Hajda , Neil Armstrong , Robert Foss , Laurent Pinchart , Jonas Karlman , Jernej Skrabec , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Bryan O'Donoghue , Guenter Roeck , Janne Grunau , Simon Ser , Andy Gross , Bjorn Andersson , Konrad Dybcio , Greg Kroah-Hartman , dri-devel@lists.freedesktop.org, linux-arm-msm@vger.kernel.org, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, freedreno@lists.freedesktop.org, Won Chung References: <20230903214150.2877023-1-dmitry.baryshkov@linaro.org> <20230903214150.2877023-2-dmitry.baryshkov@linaro.org> From: Dmitry Baryshkov In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/09/2023 16:38, Heikki Krogerus wrote: > On Wed, Sep 06, 2023 at 03:48:35PM +0300, Dmitry Baryshkov wrote: >> On Wed, 6 Sept 2023 at 15:44, Heikki Krogerus >> wrote: >>> >>> On Tue, Sep 05, 2023 at 01:56:59PM +0300, Dmitry Baryshkov wrote: >>>> Hi Heikki, >>>> >>>> On Tue, 5 Sept 2023 at 11:50, Heikki Krogerus >>>> wrote: >>>>> >>>>> Hi Dmitry, >>>>> >>>>> On Mon, Sep 04, 2023 at 12:41:39AM +0300, Dmitry Baryshkov wrote: >>>>>> The kdev->fwnode pointer is never set in drm_sysfs_connector_add(), so >>>>>> dev_fwnode() checks never succeed, making the respective commit NOP. >>>>> >>>>> That's not true. The dev->fwnode is assigned when the device is >>>>> created on ACPI platforms automatically. If the drm_connector fwnode >>>>> member is assigned before the device is registered, then that fwnode >>>>> is assigned also to the device - see drm_connector_acpi_find_companion(). >>>>> >>>>> But please note that even if drm_connector does not have anything in >>>>> its fwnode member, the device may still be assigned fwnode, just based >>>>> on some other logic (maybe in drivers/acpi/acpi_video.c?). >>>>> >>>>>> And if drm_sysfs_connector_add() is modified to set kdev->fwnode, it >>>>>> breaks drivers already using components (as it was pointed at [1]), >>>>>> resulting in a deadlock. Lockdep trace is provided below. >>>>>> >>>>>> Granted these two issues, it seems impractical to fix this commit in any >>>>>> sane way. Revert it instead. >>>>> >>>>> I think there is already user space stuff that relies on these links, >>>>> so I'm not sure you can just remove them like that. If the component >>>>> framework is not the correct tool here, then I think you need to >>>>> suggest some other way of creating them. >>>> >>>> The issue (that was pointed out during review) is that having a >>>> component code in the framework code can lead to lockups. With the >>>> patch #2 in place (which is the only logical way to set kdev->fwnode >>>> for non-ACPI systems) probing of drivers which use components and set >>>> drm_connector::fwnode breaks immediately. >>>> >>>> Can we move the component part to the respective drivers? With the >>>> patch 2 in place, connector->fwnode will be copied to the created >>>> kdev's fwnode pointer. >>>> >>>> Another option might be to make this drm_sysfs component registration optional. >>> >>> You don't need to use the component framework at all if there is >>> a better way of determining the connection between the DP and its >>> Type-C connector (I'm assuming that that's what this series is about). >>> You just need the symlinks, not the component. >> >> The problem is that right now this component registration has become >> mandatory. And if I set the kdev->fwnode manually (like in the patch >> 2), the kernel hangs inside the component code. >> That's why I proposed to move the components to the place where they >> are really necessary, e.g. i915 and amd drivers. > > So why can't we replace the component with the method you are > proposing in this series of finding out the Type-C port also with > i915, AMD, or whatever driver and platform (that's the only thing that > component is used for)? The drm/msm driver uses drm_bridge for the pipeline (including the last DP entry) and the drm_bridge_connector to create the connector. I think that enabling i915 and AMD drivers to use drm_bridge fells out of scope for this series. > Determining the connection between a DP and its Type-C connector is > starting to get really important, so ideally we have a common solution > for that. Yes. This is what we have been discussing with Simon for quite some time on #dri-devel. Unfortunately I think the solution that got merged was pretty much hastened in instead of being well-thought. For example, it is also not always possible to provide the drm_connector / typec_connector links (as you can see from the patch7. Sometimes we can only express that this is a Type-C DP connector, but we can not easily point it to the particular USB-C port. So, I'm not sure, how can we proceed here. Currently merged patch breaks drm/msm if we even try to use it by setting kdef->fwnode to drm_connector->fwnode. The pointed out `drivers/usb/typec/port-mapper.c` is an ACPI-only thing, which is not expected to work in a non-ACPI cases. -- With best wishes Dmitry