From: Maxime Ripard <maxime.ripard@bootlin.com>
To: Icenowy Zheng <icenowy@aosc.io>
Cc: devicetree@vger.kernel.org, Dave Airlie <airlied@linux.ie>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
dri-devel <dri-devel@lists.freedesktop.org>,
linux-sunxi <linux-sunxi@googlegroups.com>,
Rob Herring <robh+dt@kernel.org>,
Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
Chen-Yu Tsai <wens@csie.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 9/9] [DO NOT MERGE] drm/sun4i: rgb: Add 5% tolerance to dot clock frequency check
Date: Thu, 18 Oct 2018 15:07:49 +0200 [thread overview]
Message-ID: <20181018130749.jkcda4epfb3xshvi@flea> (raw)
In-Reply-To: <0c8e2417ec79b44d88a3054d0526bfc5abb364d6.camel@aosc.io>
On Thu, Oct 18, 2018 at 08:50:15PM +0800, Icenowy Zheng wrote:
> 在 2018-10-18四的 14:18 +0200,Maxime Ripard写道:
> > On Thu, Oct 18, 2018 at 02:31:01PM +0300, Laurent Pinchart wrote:
> > > Hello,
> > >
> > > On Thursday, 18 October 2018 12:42:58 EEST Maxime Ripard wrote:
> > > > On Thu, Oct 18, 2018 at 11:18:06AM +0200, Daniel Vetter wrote:
> > > > > On Thu, Oct 18, 2018 at 10:55 AM Laurent Pinchart wrote:
> > > > > > On Thursday, 18 October 2018 10:33:27 EEST Icenowy Zheng
> > > > > > wrote:
> > > > > > > From: Chen-Yu Tsai <wens@csie.org>
> > > > > > >
> > > > > > > The panels shipped with Allwinner devices are very
> > > > > > > "generic", i.e.
> > > > > > > they do not have model numbers or reliable sources of
> > > > > > > information
> > > > > > > for the timings (that we know of) other than the fex files
> > > > > > > shipped
> > > > > > > on them. The dot clock frequency provided in the fex files
> > > > > > > have all
> > > > > > > been rounded to the nearest MHz, as that is the unit used
> > > > > > > in them.
> > > > > > >
> > > > > > > We were using the simple panel "urt,umsh-8596md-t" as a
> > > > > > > substitute
> > > > > > > for the A13 Q8 tablets in the absence of a specific model
> > > > > > > for what
> > > > > > > may be many different but otherwise timing compatible
> > > > > > > panels. This
> > > > > > > was usable without any visual artifacts or side effects,
> > > > > > > until the
> > > > > > > dot clock rate check was added in commit bb43d40d7c83
> > > > > > > ("drm/sun4i:
> > > > > > > rgb: Validate the clock rate").
> > > > > > >
> > > > > > > The reason this check fails is because the dotclock
> > > > > > > frequency for
> > > > > > > this model is 33.26 MHz, which is not achievable with our
> > > > > > > dot clock
> > > > > > > hardware, and the rate returned by clk_round_rate deviates
> > > > > > > slightly,
> > > > > > > causing the driver to reject the display mode.
> > > > > > >
> > > > > > > The LCD panels have some tolerance on the dot clock
> > > > > > > frequency, even
> > > > > > > if it's not specified in their datasheets.
> > > > > > >
> > > > > > > This patch adds a 5% tolerence to the dot clock check.
> > > > > >
> > > > > > Why do you think this shouldn't be merged ?
> > > > >
> > > > > It pisses of a lot of people who really insist upon accurate
> > > > > timing.
> > > >
> > > > It's not just about accurate timings. That 5% is a made-up limit,
> > > > that
> > > > never have really been confirmed by looking at the typical
> > > > tolerancies
> > > > of panels.
> > > >
> > > > And while being to relaxed might make some panels work that are
> > > > not
> > > > working currently, it might also break some panels that currently
> > > > work
> > > > and won't now, and ideally, we should really be able to let those
> > > > panels work if they can, and filter out resolutions if they
> > > > can't.
> > > >
> > > > > I think a better fix would be to have a dotclock range in
> > > > > drm_panel,
> > > > > and some magic to figure out which one of these we can actually
> > > > > do. Then tell userspace that this is the mode is should
> > > > > request. That way userspace knows what the actual
> > > > > dotclock/refresh
> > > > > rate is, and the panel still works.
> > > >
> > > > It's not just about panels, but also bridges with EDID where the
> > > > tolerancy is not exposed.
> > >
> > > Given that the tolerance is a property of the panel or bridge, I
> > > agree with
> > > Daniel that it should be implemented there, or at least in
> > > cooperation with
> > > drm_panel and drm_bridge.
> >
> > How are we supposed to deal with panels without any documentation
> > then?
> >
> > > Semi-related information, I think the CEA and VESA standards allow
> > > a 0.5%
> > > clock tolerance. What is the maximum clock frequency deviation
> > > required for
> > > this platform ?
> >
> > Looks like it does indeed. That's definetely good to know.
>
> Then maybe we can choose to allow 0.5% error when a bridge is attached?
It doesn't fix the panel case, but that sounds reasonable yes
Maxime
--
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
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next prev parent reply other threads:[~2018-10-18 13:08 UTC|newest]
Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-18 7:33 [PATCH 0/9] Analogix ANX6345 RGB-(e)DP bridge support Icenowy Zheng
2018-10-18 7:33 ` [PATCH 4/9] dt-bindings: Add ANX6345 DP/eDP transmitter binding Icenowy Zheng
[not found] ` <20181018073327.64942-5-icenowy-h8G6r0blFSE@public.gmane.org>
2018-10-18 8:53 ` Laurent Pinchart
2018-10-18 10:00 ` Icenowy Zheng
[not found] ` <c68f0da9607805e1f6673a9a16a7dcfff4d8fe91.camel-h8G6r0blFSE@public.gmane.org>
2018-10-18 11:23 ` Laurent Pinchart
2018-10-18 12:40 ` Icenowy Zheng
[not found] ` <f71d442412f31828c466e3483e9d42f5e96ddc1d.camel-h8G6r0blFSE@public.gmane.org>
2018-10-25 18:30 ` Rob Herring
2018-10-26 0:08 ` Icenowy Zheng
2018-10-18 7:33 ` [PATCH 6/9] arm64: allwinner: a64: add pinmux for RGB666 LCD Icenowy Zheng
2018-10-18 7:33 ` [PATCH 7/9] arm64: allwinner: a64: enable ANX6345 bridge on Pinebook Icenowy Zheng
2018-10-18 15:17 ` Vasily Khoruzhick
2018-10-19 5:50 ` Icenowy Zheng
2018-10-18 7:33 ` [PATCH 8/9] arm64: allwinner: a64: enable ANX6345 bridge on TERES-I Icenowy Zheng
[not found] ` <20181018073327.64942-1-icenowy-h8G6r0blFSE@public.gmane.org>
2018-10-18 7:33 ` [PATCH 1/9] drm/bridge: move ANA78xx driver to analogix subdirectory Icenowy Zheng
[not found] ` <20181018073327.64942-2-icenowy-h8G6r0blFSE@public.gmane.org>
2018-10-18 8:47 ` Laurent Pinchart
2018-10-18 7:33 ` [PATCH 2/9] drm/bridge: split some definitions of ANX78xx to dedicated headers Icenowy Zheng
2018-10-18 7:33 ` [PATCH 3/9] drm/bridge: extract some Analogix I2C DP common code Icenowy Zheng
2018-10-18 7:33 ` [PATCH 5/9] drm/bridge: Add Analogix anx6345 support Icenowy Zheng
2018-10-18 7:33 ` [PATCH 9/9] [DO NOT MERGE] drm/sun4i: rgb: Add 5% tolerance to dot clock frequency check Icenowy Zheng
[not found] ` <20181018073327.64942-10-icenowy-h8G6r0blFSE@public.gmane.org>
2018-10-18 8:55 ` Laurent Pinchart
2018-10-18 9:18 ` Daniel Vetter
[not found] ` <CAKMK7uFp2c=wqzPi096MTRB6Cdfacerkp6dM=fEqCAr99PQG9w-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2018-10-18 9:42 ` Maxime Ripard
2018-10-18 11:31 ` Laurent Pinchart
2018-10-18 12:18 ` Maxime Ripard
2018-10-18 12:50 ` Icenowy Zheng
2018-10-18 13:07 ` Maxime Ripard [this message]
2018-10-18 13:57 ` Laurent Pinchart
2019-02-03 1:32 ` Vasily Khoruzhick
2018-10-18 12:25 ` Stefan Monnier
2018-10-29 2:20 ` [PATCH 0/9] Analogix ANX6345 RGB-(e)DP bridge support Vasily Khoruzhick
2019-02-04 12:22 ` Torsten Duwe
[not found] ` <20190204122250.GB7660-jcswGhMUV9g@public.gmane.org>
2019-02-04 20:21 ` Vasily Khoruzhick
2019-02-03 18:54 [PATCH RESEND v2 00/12] " Vasily Khoruzhick
[not found] ` <20190203185501.8958-1-anarsoul-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2019-02-03 18:54 ` [PATCH RESEND v2 01/12] drm/bridge: move ANA78xx driver to analogix subdirectory Vasily Khoruzhick
2019-02-03 18:54 ` [PATCH RESEND v2 02/12] drm/bridge: split some definitions of ANX78xx to dedicated headers Vasily Khoruzhick
2019-02-03 18:54 ` [PATCH RESEND v2 03/12] drm/bridge: extract some Analogix I2C DP common code Vasily Khoruzhick
2019-02-03 18:54 ` [PATCH RESEND v2 04/12] dt-bindings: Add ANX6345 DP/eDP transmitter binding Vasily Khoruzhick
2019-02-03 18:54 ` [PATCH RESEND v2 05/12] drm/bridge: Add Analogix anx6345 support Vasily Khoruzhick
2019-02-05 13:19 ` Torsten Duwe
2019-02-03 18:54 ` [PATCH RESEND v2 06/12] drm/sun4i: rgb: Add 1% tolerance to dclk frequency check when bridge is connected Vasily Khoruzhick
[not found] ` <20190203185501.8958-7-anarsoul-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2019-02-04 14:20 ` Maxime Ripard
2019-02-04 16:26 ` Vasily Khoruzhick
[not found] ` <CA+E=qVfTfJ9E29gz83tdVGx5_KGWSQVJOAxKTzC+-n7=gdj0cA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2019-02-04 16:28 ` Icenowy Zheng
[not found] ` <0F6CBEA4-6DB6-40F1-A2FD-65101AF64F1F-h8G6r0blFSE@public.gmane.org>
2019-02-04 18:50 ` Vasily Khoruzhick
[not found] ` <CA+E=qVd7yh=JNZSvrfY4Diu+VJWFK6yLUJ5MavBcZ8Cftn6f-Q-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2019-02-05 15:41 ` Maxime Ripard
2019-02-05 17:49 ` Vasily Khoruzhick
2019-02-06 9:16 ` [linux-sunxi] " Maxime Ripard
2019-02-06 11:42 ` Thierry Reding
2019-02-03 18:54 ` [PATCH RESEND v2 07/12] drm/panel: simple: don't fail if we don't have panel desc Vasily Khoruzhick
2019-02-03 18:54 ` [PATCH RESEND v2 08/12] dt-bindings: add binding for generic eDP panel Vasily Khoruzhick
[not found] ` <20190203185501.8958-9-anarsoul-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2019-02-04 7:43 ` Thierry Reding
2019-02-04 8:13 ` Vasily Khoruzhick
[not found] ` <CA+E=qVecudACOEXt74Kf=UA_F-uuHgEqHzKpYAq1ocMx3Sx+eQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2019-02-04 8:23 ` Thierry Reding
2019-02-04 9:40 ` Daniel Vetter
[not found] ` <20190204094012.GP3271-dv86pmgwkMBes7Z6vYuT8azUEOm+Xw19@public.gmane.org>
2019-02-04 11:22 ` Thierry Reding
2019-02-04 15:59 ` Daniel Vetter
[not found] ` <20190204155909.GU3271-dv86pmgwkMBes7Z6vYuT8azUEOm+Xw19@public.gmane.org>
2019-02-04 16:22 ` Thierry Reding
2019-02-05 8:57 ` Daniel Vetter
2019-02-05 10:24 ` Thierry Reding
2019-02-05 16:36 ` Daniel Vetter
[not found] ` <20190205163649.GG3271-dv86pmgwkMBes7Z6vYuT8azUEOm+Xw19@public.gmane.org>
2019-02-14 19:51 ` Vasily Khoruzhick
2019-02-14 20:05 ` Vasily Khoruzhick
[not found] ` <CA+E=qVcUsz=5s1+RqDdQ4Hm3_Q3jDFuZwuYXUuVx3ubFWmcG7w-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2019-02-14 20:38 ` Rob Herring
[not found] ` <CAL_JsqKQ0EmyYGYvz__ZZGN7_6jLezevHWc+psn82Uy6hWZXMA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2019-02-14 20:54 ` Vasily Khoruzhick
2019-02-04 16:11 ` Vasily Khoruzhick
[not found] ` <CA+E=qVew+8__yrAud1gFnLQ8HCwDdGhVjV=c173HGvZxH=7zZQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2019-02-04 16:27 ` Thierry Reding
2019-02-04 16:39 ` Rob Herring
[not found] ` <CAL_JsqLAODca_U94hCi9O3E6XiUjAYCoL7_0gkf_eMY0nnT8Ag-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2019-02-04 17:02 ` Vasily Khoruzhick
2019-02-04 16:27 ` Rob Herring
[not found] ` <CAL_JsqKt1kOXmRNvkYsQ6AL69+TPZURKpDbKkkEUb2+KZ5hKjQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2019-02-04 16:56 ` Thierry Reding
2019-02-04 17:07 ` Vasily Khoruzhick
2019-02-04 20:23 ` Rob Herring
[not found] ` <CAL_JsqJx98DfHZSafiXA8QiO=bn1zy8g6keQ15L=cUmbVkTTOA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2019-02-04 20:26 ` Vasily Khoruzhick
2019-02-04 20:34 ` Rob Herring
2019-02-03 18:54 ` [PATCH RESEND v2 09/12] drm/panel: simple: add " Vasily Khoruzhick
2019-02-03 18:54 ` [PATCH RESEND v2 10/12] arm64: allwinner: a64: add pinmux for RGB666 LCD Vasily Khoruzhick
2019-02-03 18:55 ` [PATCH RESEND v2 11/12] arm64: allwinner: a64: enable LCD-related hardware for Pinebook Vasily Khoruzhick
2019-02-03 18:55 ` [PATCH RESEND v2 12/12] arm64: allwinner: a64: enable LCD-related hardware for TERES-I Vasily Khoruzhick
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