From: Stefan Wahren <stefan.wahren@i2se.com>
To: "Ivan T. Ivanov" <iivanov@suse.de>
Cc: Michael Turquette <mturquette@baylibre.com>,
Stephen Boyd <sboyd@kernel.org>,
Nicolas Saenz Julienne <nsaenz@kernel.org>,
Florian Fainelli <f.fainelli@gmail.com>,
Ray Jui <rjui@broadcom.com>,
Scott Branden <sbranden@broadcom.com>,
Paul Walmsley <paul.walmsley@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
Phil Elwell <phil@raspberrypi.org>,
kernel test robot <lkp@intel.com>,
bcm-kernel-feedback-list@broadcom.com, linux-clk@vger.kernel.org,
linux-rpi-kernel@lists.infradead.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] clk: bcm2835: Round UART input clock up
Date: Mon, 18 Apr 2022 18:01:31 +0200 [thread overview]
Message-ID: <6adc9c1c-ec75-b52c-9c44-00296eaa00f6@i2se.com> (raw)
In-Reply-To: <20220418113801.uree7rvkzxpiwyni@suse>
Am 18.04.22 um 13:38 schrieb Ivan T. Ivanov:
> On 04-18 13:22, Stefan Wahren wrote:
>> Hi Ivan,
>>
>> Am 18.04.22 um 13:05 schrieb Ivan T. Ivanov:
>>> Hi Stefan,
>>>
>>> On 04-15 10:52, Stefan Wahren wrote:
>>>> Hi Ivan,
>>>>
>>>> Am 14.04.22 um 12:56 schrieb Ivan T. Ivanov:
>>>>> Hi Stefan,
>>>>>
>>>>> Please, could you take a look into following patch?
>>>> yes, but i cannot give a technical review. But from my gut feeling this
>>>> doesn't look really elegant to me.
>>>>> Thanks!
>>>>> Ivan
>>>>>
>>>>> On 04-04 15:51, Ivan T. Ivanov wrote:
>>>>>> Subject: [PATCH v2] clk: bcm2835: Round UART input clock up
>>>>>> Message-Id: <20220404125113.80239-1-iivanov@suse.de>
>>>>>>
>>>>>> 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 baudrate
>>>>>> == 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.
>>>> Based on this commit message this looks like a fix / workaround for an
>>>> issue. It would be very helpful to know:
>>>>
>>>> What issue should be fixed?
>>>>
>>>> Why is it fixed here and not in the UART driver for instance?
>>> The UART driver is amba-pl011. Original fix, see below Github link,
>>> was inside pl011 module, but somehow it didn't look as the right
>>> place either. Beside that this 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.
>> thanks for your explanation. These are import information which belongs in
>> the commit log, because the motivation and the affected UART is very
>> important.
>>>> In case it fixes a regression, a Fixes tag should be necessary.
>>> I found the issue because it was reported that RPi3[1] and RPi Zero 2W
>>> boards have issues with the Bluetooth. So it turns out that when
>>> switching from initial to operation speed host and device no longer
>>> can talk each other because host uses incorrect baud rate.
>> Now i remember this issue, for the mainline kernel we decide to workaround
>> the issue by lowering the BT baudrate to 2000000 baud.
> I have workaranded this the same, at first, but then decided to look at
> vendor tree and voilà!
>
>> I didn't investigate
>> the issue further, but your approach is a better solution.
>>
>> Do you use the mainline DTS or the vendor DTS to see this issue?
>>
> For (open)SUSE we use downstream DTS.
This is popular and bad at the same time. We as the mainline kernel
developer cannot guarantee that this works as expected. A lot of issues
are caused by mixing vendor DTS with mainline kernel, so in general (not
for this specific issue) you are on your own with this approach.
I know this is a little bit off topic but except from overlay support,
can you provide a list of most missing features of the mainline kernel /
DTS?
> Do you think that if I put better description in commit message fix will
> be more acceptable.
At least it would increase the chance to be accepted. This rounding
behavior looks open coded, maybe there is already a function to achieve
this.
> Or if someone could suggest anything else I am open
> to discussion.
>
> Regards,
> Ivan
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2022-04-18 16:03 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-04 12:51 [PATCH v2] clk: bcm2835: Round UART input clock up Ivan T. Ivanov
2022-04-14 10:56 ` Ivan T. Ivanov
2022-04-15 8:52 ` Stefan Wahren
2022-04-18 11:05 ` Ivan T. Ivanov
2022-04-18 11:22 ` Stefan Wahren
2022-04-18 11:38 ` Ivan T. Ivanov
2022-04-18 16:01 ` Stefan Wahren [this message]
2022-04-19 15:05 ` Ivan T. Ivanov
2022-04-19 16:11 ` Stefan Wahren
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=6adc9c1c-ec75-b52c-9c44-00296eaa00f6@i2se.com \
--to=stefan.wahren@i2se.com \
--cc=aou@eecs.berkeley.edu \
--cc=bcm-kernel-feedback-list@broadcom.com \
--cc=f.fainelli@gmail.com \
--cc=iivanov@suse.de \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-clk@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-rpi-kernel@lists.infradead.org \
--cc=lkp@intel.com \
--cc=mturquette@baylibre.com \
--cc=nsaenz@kernel.org \
--cc=palmer@dabbelt.com \
--cc=paul.walmsley@sifive.com \
--cc=phil@raspberrypi.org \
--cc=rjui@broadcom.com \
--cc=sboyd@kernel.org \
--cc=sbranden@broadcom.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).