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Mon, 26 Sep 2022 08:43:01 -0400 (EDT) Date: Mon, 26 Sep 2022 14:42:59 +0200 From: Maxime Ripard To: Thomas Zimmermann Cc: Geert Uytterhoeven , Karol Herbst , David Airlie , nouveau@lists.freedesktop.org, dri-devel@lists.freedesktop.org, Phil Elwell , Emma Anholt , Samuel Holland , Jernej Skrabec , Chen-Yu Tsai , Ben Skeggs , linux-sunxi@lists.linux.dev, intel-gfx@lists.freedesktop.org, Hans de Goede , Rodrigo Vivi , linux-arm-kernel@lists.infradead.org, Tvrtko Ursulin , Dom Cobley , Dave Stevenson , linux-kernel@vger.kernel.org, Mateusz Kwiatkowski , Noralf =?utf-8?Q?Tr=C3=B8nnes?= Subject: Re: [PATCH v2 10/33] drm/modes: Add a function to generate analog display modes Message-ID: <20220926124259.o6fcfnxjy7gyzqz2@houat> References: <20220728-rpi-analog-tv-properties-v2-0-f733a0ed9f90@cerno.tech> <20220728-rpi-analog-tv-properties-v2-10-f733a0ed9f90@cerno.tech> <72a8c3ce-ed03-0a77-fb92-eaa992eb86fe@suse.de> <20220926101716.urehomr2lzv5pqln@houat> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="zlfwclqmvthsubza" Content-Disposition: inline In-Reply-To: X-Spam-Status: No, score=-2.8 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_LOW,SPF_HELO_PASS, SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --zlfwclqmvthsubza Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Sep 26, 2022 at 01:17:52PM +0200, Thomas Zimmermann wrote: > Hi >=20 > Am 26.09.22 um 12:34 schrieb Geert Uytterhoeven: > > Hi Maxime, > >=20 > > On Mon, Sep 26, 2022 at 12:17 PM Maxime Ripard wrot= e: > > > On Fri, Sep 23, 2022 at 11:05:48AM +0200, Thomas Zimmermann wrote: > > > > > + /* 63.556us * 13.5MHz =3D 858 pixels */ > > > >=20 > > > > I kind of get what the comment wants to tell me, but the units don'= t add up. > > >=20 > > > I'm not sure how it doesn't add up? > > >=20 > > > We have a frequency in Hz (equivalent to s^-1) and a duration in s, so > > > the result ends up with no dimension, which is to be expected for a > > > number of periods? > >=20 > > To make the units add up, it should be 13.5 Mpixel/s > > (which is what a pixel clock of 13.5 MHz really means ;-) >=20 > Sort of. It leaves the time value as a magic number, which obfuscates wha= t's > happening. >=20 > The unit for htotal is pixels/scanline because if you multiply it with the > number of scanlines per frame (which is in vtotal), you get pixels/frame. > Multiplying with the frames per second results in the pixel clock in > pixels/second. That's true, but both are true? > That's a bit much for this comment. Hence, I suggested to remove these > comments entirely and document the relation among the numbers in a more > prominent location. The documentation for drm_display_mode would be a good > place, I guess. I'm not sure I understand what it's about. It's an explicit requirement of PAL and NTSC, why would something so specific be in the generic definition of drm_display_mode? Maxime --zlfwclqmvthsubza Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQRcEzekXsqa64kGDp7j7w1vZxhRxQUCYzGeUwAKCRDj7w1vZxhR xY5tAP9KJjA2OGdWz1GFAUwsCyA+v6gay+4c8P+X8ZcLHAES9QEAx6aTDtrTd2Yz yzAZ6N+Br4689AWFKhh40XQtNNC5JQE= =nm5h -----END PGP SIGNATURE----- --zlfwclqmvthsubza--