linux-kernel - Re: [PATCH v5 80/80] ARM: dts: bcm2711: Enable the display pipeline

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Date:   Thu, 01 Oct 2020 11:22:03 +0200
From:   Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
To:     Nathan Chancellor <natechancellor@...il.com>,
        Maxime Ripard <maxime@...no.tech>
Cc:     Eric Anholt <eric@...olt.net>,
        Stefan Wahren <stefan.wahren@...e.com>,
        Tim Gover <tim.gover@...pberrypi.com>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Hoegeun Kwon <hoegeun.kwon@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        bcm-kernel-feedback-list@...adcom.com,
        linux-rpi-kernel@...ts.infradead.org,
        Phil Elwell <phil@...pberrypi.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v5 80/80] ARM: dts: bcm2711: Enable the display pipeline

On Wed, 2020-09-30 at 09:38 -0700, Nathan Chancellor wrote:
> On Wed, Sep 30, 2020 at 04:07:58PM +0200, Maxime Ripard wrote:
> > Hi Nathan,
> > 
> > On Tue, Sep 29, 2020 at 03:15:26PM -0700, Nathan Chancellor wrote:
> > > On Thu, Sep 03, 2020 at 10:01:52AM +0200, Maxime Ripard wrote:
> > > > Now that all the drivers have been adjusted for it, let's bring in the
> > > > necessary device tree changes.
> > > > 
> > > > The VEC and PV3 are left out for now, since it will require a more specific
> > > > clock setup.
> > > > 
> > > > Reviewed-by: Dave Stevenson <dave.stevenson@...pberrypi.com>
> > > > Tested-by: Chanwoo Choi <cw00.choi@...sung.com>
> > > > Tested-by: Hoegeun Kwon <hoegeun.kwon@...sung.com>
> > > > Tested-by: Stefan Wahren <stefan.wahren@...e.com>
> > > > Signed-off-by: Maxime Ripard <maxime@...no.tech>
> > > 
> > > Apologies if this has already been reported or have a solution but this
> > > patch (and presumably series) breaks output to the serial console after
> > > a certain point during init. On Raspbian, I see systemd startup messages
> > > then the output just turns into complete garbage. It looks like this
> > > patch is merged first in linux-next, which is why my bisect fell on the
> > > DRM merge. I am happy to provide whatever information could be helpful
> > > for debugging this. I am on the latest version of the firmware
> > > (currently 26620cc9a63c6cb9965374d509479b4ee2c30241).
> > 
> > Unfortunately, the miniUART is in the same clock tree than the core
> > clock and will thus have those kind of issues when the core clock is
> > changed (which is also something that one should expect when using the
> > DRM or other drivers).
> > 
> > The only real workaround there would be to switch to one of the PL011
> > UARTs. I guess we can also somehow make the UART react to the core clock
> > frequency changes, but that's going to require some effort
> > 
> > Maxime
> 
> Ack, thank you for the reply! There does not really seem to be a whole
> ton of documentation around using one of the other PL011 UARTs so for
> now, I will just revert this commit locally.

Nathan, a less intrusive solution would be to add 'core_freq_min=500' into your
config.txt.

Funnily enough core_freq=500 doesn't seem to work in that regard. It might be
related with what Maxime is commenting.

Regards,
Nicolas


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