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

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Message-ID: <cacbaef2-4221-50d8-3c5d-efab9f1a9c04@i2se.com>
Date:   Wed, 30 Sep 2020 18:52:13 +0200
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     Nathan Chancellor <natechancellor@...il.com>,
        Maxime Ripard <maxime@...no.tech>
Cc:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Eric Anholt <eric@...olt.net>,
        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

Hi,

Am 30.09.20 um 18:38 schrieb Nathan Chancellor:
> 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.

there was a patch series & discussion about this topic, but we finally
didn't find a rock solid solution.

You can have a look at "[RFC 5/5] serial: 8250: bcm2835aux: add notifier
to follow clock changes" from 3.4.2019 on linux-rpi-kernel.

Best regards

>
> Cheers,
> Nathan