linux-kernel - Re: [PATCH v2] clk: bcm2835: Do not use prediv with bcm2711's PLLs

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Message-ID: <20200731020553.GA3762310@ubuntu-n2-xlarge-x86>
Date:   Thu, 30 Jul 2020 19:05:53 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        bcm-kernel-feedback-list@...adcom.com,
        Eric Anholt <eric@...olt.net>,
        Stefan Wahren <wahrenst@....net>,
        Matthias Brugger <mbrugger@...e.com>, pbrobinson@...il.com,
        kernel-list@...pberrypi.com,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, linux-clk@...r.kernel.org,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] clk: bcm2835: Do not use prediv with bcm2711's PLLs

On Thu, Jul 30, 2020 at 08:26:19PM +0200, Nicolas Saenz Julienne wrote:
> Contrary to previous SoCs, bcm2711 doesn't have a prescaler in the PLL
> feedback loop. Bypass it by zeroing fb_prediv_mask when running on
> bcm2711.
> 
> Note that, since the prediv configuration bits were re-purposed, this
> was triggering miscalculations on all clocks hanging from the VPU clock,
> notably the aux UART, making its output unintelligible.
> 
> Fixes: 42de9ad400af ("clk: bcm2835: Add BCM2711_CLOCK_EMMC2 support")
> Reported-by: Nathan Chancellor <natechancellor@...il.com>
> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>

I updated to the latest version of the firmware
(668419cb9876474053574b2b1dc20ca996e14cc8) and my serial console
works :) thank you for the quick fix!

Tested-by: Nathan Chancellor <natechancellor@...il.com>