linux-kernel - Re: [PATCH v2 1/3] drm/modes: introduce drm_mode_validate

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Message-ID: <ycvevzp46wv4hr6ktexxjkpifav3wi4glat4a5jagghclcpagb@3jpiyehl2fn7>
Date: Tue, 26 Nov 2024 13:11:40 +0100
From: Sean Nyekjaer <sean@...nix.com>
To: Maxime Ripard <mripard@...nel.org>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, Chen-Yu Tsai <wens@...e.org>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, Samuel Holland <samuel@...lland.org>, 
	Yannick Fertre <yannick.fertre@...s.st.com>, Raphael Gallais-Pou <raphael.gallais-pou@...s.st.com>, 
	Philippe Cornu <philippe.cornu@...s.st.com>, Maxime Coquelin <mcoquelin.stm32@...il.com>, 
	Alexandre Torgue <alexandre.torgue@...s.st.com>, dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev, 
	linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH v2 1/3] drm/modes: introduce drm_mode_validate_mode()
 helper function

On Tue, Nov 26, 2024 at 01:09:10PM +0100, Maxime Ripard wrote:
> On Tue, Nov 26, 2024 at 12:34:26PM +0100, Sean Nyekjaer wrote:
> > Hi,
> > 
> > On Tue, Nov 26, 2024 at 09:38:55AM +0100, Maxime Ripard wrote:
> > > Hi,
> > > 
> > > On Tue, Nov 26, 2024 at 08:36:00AM +0100, Sean Nyekjaer wrote:
> > > > On Mon, Nov 25, 2024 at 05:00:56PM +0100, Maxime Ripard wrote:
> > > > > On Mon, Nov 25, 2024 at 02:49:26PM +0100, Sean Nyekjaer wrote:

[...]

> > > > > 
> > > > > Thanks a lot for doing that!
> > > > > 
> > > > > I wonder about the naming though (and prototype). I doesn't really
> > > > > validates a mode, but rather makes sure that a given rate is a good
> > > > > approximation of a pixel clock. So maybe something like
> > > > > drm_mode_check_pixel_clock?
> > > > 
> > > > Naming is hard :) I will use drm_mode_check_pixel_clock() for V2.
> > > > 
> > > > Would it make sense to have the pixel clock requirement as a input
> > > > parameter? For HDMI it is 0.5%
> > > 
> > > This code was only used for panels so far. It reuses the same tolerance
> > > than HDMI because we couldn't come up with anything better, but it
> > > should totally apply to other things.
> > > 
> > > > and in my case the LVDS panel 10%.
> > > 
> > > 10% is a lot, and I'm not sure we'll want that. The framerate being
> > > anywhere between 54 and 66 fps will trip a lot of applications too.
> > > 
> > > Why do you need such a big tolerance?
> > 
> > I don't need it, it was just from the datasheet for the LVDS panel :)
> 
> So you mean the panel accepts a pixel clock within +/- 10%?

Yes :)

> 
> That makes sense, but then we should also adjust the mode timings to
> match so we still keep 60fps. There's much more to *that* than the
> helpers you try to create though, so let's keep it aside for now.

Ok

> 
> Maxime

/Sean