linux-kernel - Re: [PATCH 6.10] drm/amd/display: Refactor function dm_dp_mst_is_port_support

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Message-ID: <2024081800-owl-girdle-fd89@gregkh>
Date: Sun, 18 Aug 2024 07:08:39 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Kevin Holm <kevin@...m.dev>
Cc: stable@...r.kernel.org, regressions@...ts.linux.dev,
	amd-gfx@...ts.freedesktop.org,
	ML dri-devel <dri-devel@...ts.freedesktop.org>,
	LKML <linux-kernel@...r.kernel.org>, Wayne Lin <wayne.lin@....com>,
	Jerry Zuo <jerry.zuo@....com>,
	Zaeem Mohamed <zaeem.mohamed@....com>,
	Daniel Wheeler <daniel.wheeler@....com>,
	Alex Deucher <alexander.deucher@....com>
Subject: Re: [PATCH 6.10] drm/amd/display: Refactor function
 dm_dp_mst_is_port_support_mode()

On Sat, Aug 17, 2024 at 10:30:41PM +0200, Kevin Holm wrote:
> 
> 
> On 17.08.24 10:42, Greg KH wrote:
> > On Tue, Jul 30, 2024 at 08:53:39PM +0200, Kevin Holm wrote:
> > > From: Wayne Lin <wayne.lin@....com>
> > > 
> > > [ Upstream commit fa57924c76d995e87ca3533ec60d1d5e55769a27 ]
> > > 
> > > [Why]
> > > dm_dp_mst_is_port_support_mode() is a bit not following the original design rule and cause
> > > light up issue with multiple 4k monitors after mst dsc hub.
> > > 
> > > [How]
> > > Refactor function dm_dp_mst_is_port_support_mode() a bit to solve the light up issue.
> > > 
> > > Reviewed-by: Jerry Zuo <jerry.zuo@....com>
> > > Acked-by: Zaeem Mohamed <zaeem.mohamed@....com>
> > > Signed-off-by: Wayne Lin <wayne.lin@....com>
> > > Tested-by: Daniel Wheeler <daniel.wheeler@....com>
> > > Signed-off-by: Alex Deucher <alexander.deucher@....com>
> > > [kevin@...m.dev: Resolved merge conflict in .../amdgpu_dm_mst_types.c]
> > > Fixes: 4df96ba6676034 ("drm/amd/display: Add timing pixel encoding for mst mode validation")
> > > Link: https://lore.kernel.org/stable/d74a7768e957e6ce88c27a5bece0c64dff132e24@holm.dev/T/#u
> > > Signed-off-by: Kevin Holm <kevin@...m.dev>
> > > ---
> > > I resolved the merge conflict so that, after this patch is applied to the
> > > linux-6.10.y branch of the stable git repository, the resulting function
> > > dm_dp_mst_is_port_support_mode (and also the new function
> > > dp_get_link_current_set_bw) is identical to the original commit.
> > > 
> > > I've confirmed that it fixes the regression I reported for my use case.
> > 
> > And it turns out this change breaks the arm and arm64 builds.  I tried
> > to fix it up by applying the fixup afterward for this file, but it's
> > just too much of a mess to unwind this, so I'm going to have to revert
> > this now, sorry.
> That sucks, sorry for the problems my patch caused. :(
> 
> > See:
> > 	https://lore.kernel.org/r/b27c5434-f1b1-4697-985b-91bb3e9a22df@roeck-us.net
> > for details.
> I unfortunately don't know the amdgpu driver and kernel code in general enough to help fix
> that. The back-ported patch I send was my first patch to the kernel.
> 
> In the email thread where I reported the problem I send a patch that reverts
> 4df96ba6676034 ("drm/amd/display: Add timing pixel encoding for mst mode validation") to
> fix the problem that way [1]. I've included a copy of that below.
> I've tested that it still applies to 6.10.6-rc3 without conflicts and compiles for me. I
> could not test if the 6.10.6-rc3 with the revert applied fixes the problem as I'm
> traveling and don't have access to my normal setup. I can only say that reverting it on
> v6.10.2 fixed the problem for me.
> 
> I don't know how to compile for other architectures so I did not test that.
> 
> Not sure what would be best, reverting the problem commit so the regression is fixed in
> the 6.10 stable kernel (and maybe breaking something else?) or waiting for someone at AMD
> with better knowledge of the amdgpu driver to back-port the fixing commit in a non-broken
> way.

Yes, this is up to the amd developers now, I suggest you work with them
to get this resolved please.

Or just use 6.11-rc3 and newer :)

thanks,

greg k-h