linux-kernel - Re: [PATCH v3] clk: bcm2835: Round UART input clock up

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Date:   Wed, 24 Aug 2022 10:44:43 +0300
From:   "Ivan T. Ivanov" <iivanov@...e.de>
To:     Stephen Boyd <sboyd@...nel.org>
Cc:     Albert Ou <aou@...s.berkeley.edu>,
        Broadcom internal kernel review list 
        <bcm-kernel-feedback-list@...adcom.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Michael Turquette <mturquette@...libre.com>,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        Stefan Wahren <stefan.wahren@...e.com>,
        Phil Elwell <phil@...pberrypi.org>,
        kernel test robot <lkp@...el.com>, linux-clk@...r.kernel.org,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v3] clk: bcm2835: Round UART input clock up

On 08-23 16:08, Stephen Boyd wrote:
> Date: Tue, 23 Aug 2022 16:08:40 -0700
> From: Stephen Boyd <sboyd@...nel.org>
> To: Albert Ou <aou@...s.berkeley.edu>, Broadcom internal kernel review list
>  <bcm-kernel-feedback-list@...adcom.com>, Florian Fainelli
>  <f.fainelli@...il.com>, "Ivan T. Ivanov" <iivanov@...e.de>, Michael
>  Turquette <mturquette@...libre.com>, Nicolas Saenz Julienne
>  <nsaenz@...nel.org>, Palmer Dabbelt <palmer@...belt.com>, Paul Walmsley
>  <paul.walmsley@...ive.com>, Ray Jui <rjui@...adcom.com>, Scott Branden
>  <sbranden@...adcom.com>, Stefan Wahren <stefan.wahren@...e.com>
> Cc: "Ivan T. Ivanov" <iivanov@...e.de>, Phil Elwell <phil@...pberrypi.org>,
>  kernel test robot <lkp@...el.com>, linux-clk@...r.kernel.org,
>  linux-rpi-kernel@...ts.infradead.org,
>  linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
>  linux-riscv@...ts.infradead.org
> Subject: Re: [PATCH v3] clk: bcm2835: Round UART input clock up
> Message-Id: <20220823230842.AB8BAC433C1@...p.kernel.org>
> 
> Quoting Ivan T. Ivanov (2022-05-27 03:29:00)
> > It was reported that RPi3[1] and RPi Zero 2W boards have issues with
> > the Bluetooth. It turns out that when switching from initial to
> > operation speed host and device no longer can talk each other because
> > host uses incorrect UART baud rate.
> > 
> > The UART driver used in this case is amba-pl011. Original fix, see
> > below Github link[2], was inside pl011 module, but somehow it didn't
> > look as the right place to fix. Beside that this original rounding
> > function is not exactly perfect for all possible clock values. So I
> > deiced to move the hack to the platform which actually need it.
> > 
> > The UART clock is initialised to be as close to the requested
> > frequency as possible without exceeding it. Now that there is a
> > clock manager that returns the actual frequencies, an expected
> > 48MHz clock is reported as 47999625. If the requested baud rate
> > == requested clock/16, there is no headroom and the slight
> > reduction in actual clock rate results in failure.
> > 
> > If increasing a clock by less than 0.1% changes it from ..999..
> > to ..000.., round it up.
> > 
> > [1] https://bugzilla.suse.com/show_bug.cgi?id=1188238
> > [2] https://github.com/raspberrypi/linux/commit/ab3f1b39537f6d3825b8873006fbe2fc5ff057b7
> > 
> > Cc: Phil Elwell <phil@...pberrypi.org>
> > Signed-off-by: Ivan T. Ivanov <iivanov@...e.de>
> > ---
> 
> This is waiting for someone like Stefan to review. It's customary to
> include previous reviewers on new versions of patches.

Thanks for fixing me mistake.

Regards,
Ivan