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Wed, 15 Apr 2020 06:42:16 -0400 (EDT) Date: Wed, 15 Apr 2020 12:42:14 +0200 From: Maxime Ripard To: Jernej =?utf-8?Q?=C5=A0krabec?= Subject: Re: [PATCH] drm/sun4i: hdmi ddc clk: Fix size of m divider Message-ID: <20200415104214.ndkkxfnufkxgu53r@gilmour.lan> References: <20200413095457.1176754-1-jernej.skrabec@siol.net> <1742537.tdWV9SEqCh@jernej-laptop> MIME-Version: 1.0 In-Reply-To: <1742537.tdWV9SEqCh@jernej-laptop> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200415_034219_769942_335C8759 X-CRM114-Status: GOOD ( 17.63 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: David Airlie , linux-kernel , dri-devel , Chen-Yu Tsai , Daniel Vetter , linux-arm-kernel Content-Type: multipart/mixed; boundary="===============7296131411583405644==" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org --===============7296131411583405644== Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="iikhbqdgypmjrod7" Content-Disposition: inline --iikhbqdgypmjrod7 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Apr 13, 2020 at 06:09:08PM +0200, Jernej =C5=A0krabec wrote: > Dne ponedeljek, 13. april 2020 ob 16:12:39 CEST je Chen-Yu Tsai napisal(a= ): > > On Mon, Apr 13, 2020 at 6:11 PM Chen-Yu Tsai wrote: > > > On Mon, Apr 13, 2020 at 5:55 PM Jernej Skrabec > wrote: > > > > m divider in DDC clock register is 4 bits wide. Fix that. > > > > > > > > Fixes: 9c5681011a0c ("drm/sun4i: Add HDMI support") > > > > Signed-off-by: Jernej Skrabec > > > > > > Reviewed-by: Chen-Yu Tsai > > > > Cc stable? > > I don't think it's necessary: > 1. It doesn't change much (anything?) for me when reading EDID. I don't t= hink > it's super important to have precise DDC clock in order to properly read = EDID. > 2. No matter if it has "Cc stable" tag or not, it will be eventually pick= ed > for stable due to fixes tag. > > This was only small observation when I was researching EDID readout issue= on > A20 board, but sadly, I wasn't able to figure out why reading it sometimes > fails. I noticed similar issue on SoCs with DE2 (most prominently on Oran= gePi > PC2 - H5), but there was easy workaround - I just disabled video driver i= n U- > Boot. However, if A20 display driver gets disabled in U-Boot, it totally > breaks video output on my TV when Linux boots (no output). I guess there = is > more fundamental problem with clocks than just field size. I think we sho= uld > add more constraints in clock driver, like preset some clock parents and = not > allow to change parents when setting rate, but carefully, so simplefb doe= sn't > break. Such constraints should also solve problems with dual head setups. I disagree here. Doing all sorts of special case just doesn't scale, and we'll never have the special cases sorted out on all the boards (and it's a nightmare to maintain). Especially since it's basically putting a blanket over the actual issue and looking the other way. If there's something wrong with how we deal with (re)parenting, we should fix that. It impacts more than just DRM, and all the SoCs. Maxime --iikhbqdgypmjrod7 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQRcEzekXsqa64kGDp7j7w1vZxhRxQUCXpblBgAKCRDj7w1vZxhR xYNeAQDkWOAE17PUs/+j0UPsIutwMt3fGauL7qUSC2cDBKT12AD/Yf2YkVdEbh8n WD9IZaABcs8BR2mw6ne6+GE6MOR0Dgw= =+u0/ -----END PGP SIGNATURE----- --iikhbqdgypmjrod7-- --===============7296131411583405644== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel --===============7296131411583405644==--