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Thu, 4 Sep 2025 04:33:07 -0400 (EDT) Date: Thu, 4 Sep 2025 10:33:05 +0200 From: Niklas =?utf-8?Q?S=C3=B6derlund?= To: Isaac Scott Cc: laurent.pinchart@ideasonboard.com, rmfrfs@gmail.com, martink@posteo.de, kernel@puri.sm, mchehab@kernel.org, shawnguo@kernel.org, s.hauer@pengutronix.de, kernel@pengutronix.de, festevam@gmail.com, linux-media@vger.kernel.org, imx@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, hverkuil@kernel.org, nicolas.dufresne@collabora.com, sakari.ailus@linux.intel.com, tomi.valkeinen@ideasonboard.com, jonas@kwiboo.se, dan.scally+renesas@ideasonboard.com, m.szyprowski@samsung.com, mehdi.djait@linux.intel.com Subject: Re: [PATCH v2 1/3] media: v4l: Add helper to get number of active lanes via a pad Message-ID: <20250904083305.GB1207681@ragnatech.se> References: <20250903102243.1563527-1-isaac.scott@ideasonboard.com> <20250903102243.1563527-2-isaac.scott@ideasonboard.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20250903102243.1563527-2-isaac.scott@ideasonboard.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250904_013314_383036_7A060EE2 X-CRM114-Status: GOOD ( 23.66 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Issac, Thanks for your work. On 2025-09-03 11:22:40 +0100, Isaac Scott wrote: > Sometimes, users will not use all of the MIPI CSI 2 lanes available when > connecting to the MIPI CSI receiver of their device. Add a helper > function that checks the mbus_config for the device driver to allow > users to define the number of active data lanes through the > get_mbus_config op. > > If the driver does not implement this op, fall back to using the number > of data lanes specified in device tree. > > Signed-off-by: Isaac Scott > --- > drivers/media/v4l2-core/v4l2-common.c | 25 +++++++++++++++++++++++++ > include/media/v4l2-common.h | 1 + > 2 files changed, 26 insertions(+) > > diff --git a/drivers/media/v4l2-core/v4l2-common.c b/drivers/media/v4l2-core/v4l2-common.c > index 6e585bc76367..8683107b3704 100644 > --- a/drivers/media/v4l2-core/v4l2-common.c > +++ b/drivers/media/v4l2-core/v4l2-common.c > @@ -571,6 +571,31 @@ s64 __v4l2_get_link_freq_pad(struct media_pad *pad, unsigned int mul, > return __v4l2_get_link_freq_ctrl(sd->ctrl_handler, mul, div); > } > EXPORT_SYMBOL_GPL(__v4l2_get_link_freq_pad); > + > +unsigned int v4l2_get_active_data_lanes(const struct media_pad *pad, unsigned int dt_lanes) > +{ > + struct v4l2_mbus_config mbus_config = {}; > + struct v4l2_subdev *sd; > + unsigned int lanes; > + int ret; > + > + sd = media_entity_to_v4l2_subdev(pad->entity); > + ret = v4l2_subdev_call(sd, pad, get_mbus_config, pad->index, > + &mbus_config); > + if (ret < 0 && ret != -ENOIOCTLCMD) > + return ret; The function prototype is 'unsigned int' and here you return a signed value here. > + Maybe add a comment here that this check depends on mbus_config being zeroed at init if the call above pass with -ENOIOCTLCMD? It's not immediately clear what is going on here even tho the code is clever ;-) > + if (!mbus_config.bus.mipi_csi2.num_data_lanes) > + return dt_lanes; > + > + lanes = mbus_config.bus.mipi_csi2.num_data_lanes; > + > + if (lanes < 0 || lanes > dt_lanes) > + return -EINVAL; > + > + return lanes; > +} > +EXPORT_SYMBOL_GPL(v4l2_get_active_data_lanes); > #endif /* CONFIG_MEDIA_CONTROLLER */ > > /* > diff --git a/include/media/v4l2-common.h b/include/media/v4l2-common.h > index 0a43f56578bc..3f8937260c76 100644 > --- a/include/media/v4l2-common.h > +++ b/include/media/v4l2-common.h > @@ -584,6 +584,7 @@ int v4l2_fill_pixfmt_mp(struct v4l2_pix_format_mplane *pixfmt, u32 pixelformat, > (pad, mul, div) > s64 __v4l2_get_link_freq_pad(struct media_pad *pad, unsigned int mul, > unsigned int div); > +unsigned int v4l2_get_active_data_lanes(const struct media_pad *pad, unsigned int dt_lanes); > #else > #define v4l2_get_link_freq(handler, mul, div) \ > __v4l2_get_link_freq_ctrl(handler, mul, div) > -- > 2.43.0 > -- Kind Regards, Niklas Söderlund