Hello Maxime, Benoit, sorry for chiming in, but I'm a bit confused... On Fri, Feb 22, 2019 at 04:04:21PM +0100, Maxime Ripard wrote: > On Fri, Feb 22, 2019 at 08:54:56AM -0600, Benoit Parrot wrote: > > Maxime Ripard <maxime.ripard@xxxxxxxxxxx> wrote on Fri [2019-Feb-22 15:39:59 +0100]: > > > On Thu, Feb 21, 2019 at 10:20:20AM -0600, Benoit Parrot wrote: > > > > Hi Maxime, > > > > > > > > A couple of questions, > > > > > > > > Maxime Ripard <maxime.ripard@xxxxxxxxxxx> wrote on Thu [2018-Oct-11 04:21:00 -0500]: > > > > > The clock rate, while hardcoded until now, is actually a function of the > > > > > resolution, framerate and bytes per pixel. Now that we have an algorithm to > > > > > adjust our clock rate, we can select it dynamically when we change the > > > > > mode. > > > > > > > > > > This changes a bit the clock rate being used, with the following effect: > > > > > > > > > > +------+------+------+------+-----+-----------------+----------------+-----------+ > > > > > | Hact | Vact | Htot | Vtot | FPS | Hardcoded clock | Computed clock | Deviation | > > > > > +------+------+------+------+-----+-----------------+----------------+-----------+ > > > > > | 640 | 480 | 1896 | 1080 | 15 | 56000000 | 61430400 | 8.84 % | > > > > > | 640 | 480 | 1896 | 1080 | 30 | 112000000 | 122860800 | 8.84 % | > > > > > | 1024 | 768 | 1896 | 1080 | 15 | 56000000 | 61430400 | 8.84 % | > > > > > | 1024 | 768 | 1896 | 1080 | 30 | 112000000 | 122860800 | 8.84 % | > > > > > | 320 | 240 | 1896 | 984 | 15 | 56000000 | 55969920 | 0.05 % | > > > > > | 320 | 240 | 1896 | 984 | 30 | 112000000 | 111939840 | 0.05 % | > > > > > | 176 | 144 | 1896 | 984 | 15 | 56000000 | 55969920 | 0.05 % | > > > > > | 176 | 144 | 1896 | 984 | 30 | 112000000 | 111939840 | 0.05 % | > > > > > | 720 | 480 | 1896 | 984 | 15 | 56000000 | 55969920 | 0.05 % | > > > > > | 720 | 480 | 1896 | 984 | 30 | 112000000 | 111939840 | 0.05 % | > > > > > | 720 | 576 | 1896 | 984 | 15 | 56000000 | 55969920 | 0.05 % | > > > > > | 720 | 576 | 1896 | 984 | 30 | 112000000 | 111939840 | 0.05 % | > > > > > | 1280 | 720 | 1892 | 740 | 15 | 42000000 | 42002400 | 0.01 % | > > > > > | 1280 | 720 | 1892 | 740 | 30 | 84000000 | 84004800 | 0.01 % | > > > > > | 1920 | 1080 | 2500 | 1120 | 15 | 84000000 | 84000000 | 0.00 % | > > > > > | 1920 | 1080 | 2500 | 1120 | 30 | 168000000 | 168000000 | 0.00 % | > > > > > | 2592 | 1944 | 2844 | 1944 | 15 | 84000000 | 165862080 | 49.36 % | > > > > > +------+------+------+------+-----+-----------------+----------------+-----------+ > > > > > > > > Is the computed clock above the same for both parallel and CSI2? > > > > > > > > I want to add controls for PIXEL_RATE and LINK_FREQ, would you have any > > > > quick pointer on taking the computed clock and translating that into the > > > > PIXEL_RATE and LINK_FREQ values? > > > > > > > > I am trying to use this sensor with TI CAL driver which at the moment uses > > > > the PIXEL_RATE values in order to compute ths_settle and ths_term values > > > > needed to program the DPHY properly. This is similar in behavior as the way > > > > omap3isp relies on this info as well. > > > > > > I haven't looked that much into the csi-2 case, but the pixel rate > > > should be the same at least. > > > > I'll have to study the way the computed clock is actually calculated for > > either case, but if they yield the same number then I would be surprised > > that the pixel rate would be the same as in parallel mode you get 8 data > > bits per clock whereas in CSI2 using 2 data lanes you get 4 data bits per > > clock. > > The bus rate will be different, but the pixel rate is the same: you > have as many pixels per frames and as many frames per seconds in the > parallel and CSI cases. > I agree with that, but.. > > So just to be certain here the "Computed clock" column above would be the > > pixel clock frequency? > > it is ...it seems to me the Computed clock column is actually the "byte clock". From a simple calculation for the 640x480@15FPS case: "Computed clock" = 1896 * 1080 * 15 * 2 = 61430400 While, in my understanding, the pixel clock would just be pixel_clock = HTOT * VTOT * FPS = 1896 * 1080 * 15 = 30715200 So I suspect the "* 2" there is the number of bytes per pixel. That would match what's also reported here file:///home/jmondi/project/renesas/linux/linux-build/Documentation/output/media/kapi/csi2.html?highlight=link_freq Where: link_freq = (pixel_rate * bpp) / (2 * nr_lanes) So if I were to calculate PIXEL_RATE and LINK_FREQ in this driver, that would be: PIXEL_RATE = mode->vtot * mode->htot * ov5640_framerates[sensor->current_fr]; LINK_FREQ = PIXEL_RATE * 16 / ( 2 * sensor->ep.bus.mipi_csi2.num_data_lanes); (assuming, as the driver does now, all formats have 16bpp) Does this match your understanding as well? Thanks j > > Maxime > > -- > Maxime Ripard, Bootlin > Embedded Linux and Kernel engineering > https://bootlin.com
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