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[188.141.3.146]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-39c0dcc66a4sm12395938f8f.42.2025.04.01.01.11.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 01 Apr 2025 01:11:20 -0700 (PDT) Message-ID: <55e070e6-4f01-4db1-bbe8-f8ebc6abd6c1@linaro.org> Date: Tue, 1 Apr 2025 09:11:19 +0100 Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/2] media: i2c: ov02e10: add OV02E10 image sensor driver To: Alan Stern Cc: Sakari Ailus , Mauro Carvalho Chehab , Liam Girdwood , Mark Brown , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Bryan O'Donoghue , Hans de Goede , Jingjing Xiong , Hao Yao , Jim Lai , You-Sheng Yang , Hans de Goede , linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, devicetree@vger.kernel.org References: <20250325-b4-media-comitters-next-25-03-13-ov02e10-v2-0-4d933ac8cff6@linaro.org> <20250325-b4-media-comitters-next-25-03-13-ov02e10-v2-2-4d933ac8cff6@linaro.org> <47dd7daa-cce4-4ad0-ab57-4c76304b0aa6@linaro.org> <9c6cb27d-dd9c-4cb5-bd84-5b11ae099778@rowland.harvard.edu> Content-Language: en-US From: Bryan O'Donoghue In-Reply-To: <9c6cb27d-dd9c-4cb5-bd84-5b11ae099778@rowland.harvard.edu> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 01/04/2025 03:35, Alan Stern wrote: > On Tue, Apr 01, 2025 at 01:34:29AM +0100, Bryan O'Donoghue wrote: >> On 27/03/2025 07:36, Sakari Ailus wrote: >>>> +static u64 to_pixel_rate(u32 f_index) >>>> +{ >>>> + u64 pixel_rate = link_freq_menu_items[f_index] * 2 * OV02E10_DATA_LANES; >>>> + >>>> + do_div(pixel_rate, OV02E10_RGB_DEPTH); >>> The pixel rate control is for the pixel rate on the pixel array, not on the >>> CSI-2 interface. Without binning or sub-sampling these may the same still, >>> but this only works in special cases really. >> >> Hmm computer says no, I don't think I have understood this comment.. >> >> Looking at other drivers, I'd say the above pattern is pretty common - >> taking ov8856 as an example that's pretty much equivalent logic to the >> above, ov08x40 does something similar. >> >> => >> >> pixel_rate == link_freq * 2 * #oflanes / RGB_DEPTH >> => 360MHz * 2 * 2 / 10 >> => 360000000 * 2 * 2 / 10 >> => 144000000 >> >> If I'm understanding you though you mean the pixel rate for the control >> V4L2_CID_PIXEL_RATE expressed here should be the resolution * the FPS / >> bits_per_pixel >> >> pixel_rate = wdith x height x fps / bpp >> => 1928 * 1088 * 30 / 10 >> => 6292992 >> >> i.e. the pixel rate not related to the CSI2 link frequency ? > > I know practically nothing about this stuff, but even I can see that this > suggestion doesn't make sense: > > width x height = pixels per frame; > pixels per frame x fps = pixels per second; > pixels per second / bits per pixel = pixels^2 / (bits x seconds) > > which is meaningless. If the division were replaced with a > multiplication this would become: > > pixels per second x bits per pixel = bits per second > > which at least is reasonable. > > Alan TBH Perplexity.ai gave me that answer, my question is still are we saying the upstream examples are wrong here or have I just not understood the original comment ? --- bod