All of lore.kernel.org
 help / color / mirror / Atom feed
From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Lukas Wunner <lukas@wunner.de>
Cc: Serge Semin <Sergey.Semin@baikalelectronics.ru>,
	Daniel Winkler <danielwinkler@google.com>,
	Serge Semin <fancer.lancer@gmail.com>,
	linux-serial@vger.kernel.org, linux-mediatek@lists.infradead.org,
	Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>,
	BlueZ <linux-bluetooth@vger.kernel.org>,
	chromeos-bluetooth-upstreaming 
	<chromeos-bluetooth-upstreaming@chromium.org>,
	stable@vger.kernel.org, abhishekpandit@chromium.org,
	Aaron Sierra <asierra@xes-inc.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jslaby@suse.com>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 0/1] Revert "serial: 8250: Fix max baud limit in generic 8250 port"
Date: Thu, 2 Jul 2020 11:46:53 +0300	[thread overview]
Message-ID: <20200702084653.GG3703480@smile.fi.intel.com> (raw)
In-Reply-To: <20200702041152.e5csvbodojzwnagx@wunner.de>

On Thu, Jul 02, 2020 at 06:11:52AM +0200, Lukas Wunner wrote:
> On Thu, Jul 02, 2020 at 01:37:13AM +0300, Serge Semin wrote:
> > 1) Add a new capability like UART_CAP_NO16DIV and take it into account
> >    in the serial8250_get_baud_rate() method.
> >  
> > I don't have a documentation for the Mediatek UART port, but it seems to me
> > that that controller calculates the baud rate differently from the standard
> > 8250 port. A standard 8250 port does that by the next formulae:
> >   baud = uartclk / (16 * divisor).
> > While it seems to me that the Mediatek port uses the formulae like:
> >   baud = uartclk / divisor. (Please, correct me if I'm wrong)
> 
> 8250_bcm2835aux.c seems to suffer from a similar issue and
> solves it like this in the ->probe hook:
> 
> 	/* the HW-clock divider for bcm2835aux is 8,
> 	 * but 8250 expects a divider of 16,
> 	 * so we have to multiply the actual clock by 2
> 	 * to get identical baudrates.
> 	 */
> 	up.port.uartclk = clk_get_rate(data->clk) * 2;

8250_mid for example lies about UART clock due to this. It has a comment in the
code in its ->set_termios().

Yes, we have a lot of possibilities here to fix, I guess. We have custom
termios callback, also get and set divisor and so on.

-- 
With Best Regards,
Andy Shevchenko



WARNING: multiple messages have this Message-ID (diff)
From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Lukas Wunner <lukas@wunner.de>
Cc: chromeos-bluetooth-upstreaming
	<chromeos-bluetooth-upstreaming@chromium.org>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jslaby@suse.com>,
	linux-kernel@vger.kernel.org,
	Serge Semin <fancer.lancer@gmail.com>,
	Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>,
	Serge Semin <Sergey.Semin@baikalelectronics.ru>,
	BlueZ <linux-bluetooth@vger.kernel.org>,
	linux-mediatek@lists.infradead.org, stable@vger.kernel.org,
	linux-serial@vger.kernel.org,
	Daniel Winkler <danielwinkler@google.com>,
	abhishekpandit@chromium.org, Aaron Sierra <asierra@xes-inc.com>
Subject: Re: [PATCH v2 0/1] Revert "serial: 8250: Fix max baud limit in generic 8250 port"
Date: Thu, 2 Jul 2020 11:46:53 +0300	[thread overview]
Message-ID: <20200702084653.GG3703480@smile.fi.intel.com> (raw)
In-Reply-To: <20200702041152.e5csvbodojzwnagx@wunner.de>

On Thu, Jul 02, 2020 at 06:11:52AM +0200, Lukas Wunner wrote:
> On Thu, Jul 02, 2020 at 01:37:13AM +0300, Serge Semin wrote:
> > 1) Add a new capability like UART_CAP_NO16DIV and take it into account
> >    in the serial8250_get_baud_rate() method.
> >  
> > I don't have a documentation for the Mediatek UART port, but it seems to me
> > that that controller calculates the baud rate differently from the standard
> > 8250 port. A standard 8250 port does that by the next formulae:
> >   baud = uartclk / (16 * divisor).
> > While it seems to me that the Mediatek port uses the formulae like:
> >   baud = uartclk / divisor. (Please, correct me if I'm wrong)
> 
> 8250_bcm2835aux.c seems to suffer from a similar issue and
> solves it like this in the ->probe hook:
> 
> 	/* the HW-clock divider for bcm2835aux is 8,
> 	 * but 8250 expects a divider of 16,
> 	 * so we have to multiply the actual clock by 2
> 	 * to get identical baudrates.
> 	 */
> 	up.port.uartclk = clk_get_rate(data->clk) * 2;

8250_mid for example lies about UART clock due to this. It has a comment in the
code in its ->set_termios().

Yes, we have a lot of possibilities here to fix, I guess. We have custom
termios callback, also get and set divisor and so on.

-- 
With Best Regards,
Andy Shevchenko



_______________________________________________
Linux-mediatek mailing list
Linux-mediatek@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-mediatek

  reply	other threads:[~2020-07-02  8:47 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-01 21:13 [PATCH v2 0/1] Revert "serial: 8250: Fix max baud limit in generic 8250 port" Daniel Winkler
2020-07-01 21:13 ` Daniel Winkler
2020-07-01 21:13 ` [PATCH v2 1/1] " Daniel Winkler
2020-07-01 21:13   ` Daniel Winkler
2020-07-02  7:36   ` Greg Kroah-Hartman
2020-07-02  7:36     ` Greg Kroah-Hartman
2020-07-01 22:37 ` [PATCH v2 0/1] " Serge Semin
2020-07-01 22:37   ` Serge Semin
2020-07-02  4:11   ` Lukas Wunner
2020-07-02  8:46     ` Andy Shevchenko [this message]
2020-07-02  8:46       ` Andy Shevchenko
2020-07-02  7:37   ` Greg Kroah-Hartman
2020-07-02  7:37     ` Greg Kroah-Hartman

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=20200702084653.GG3703480@smile.fi.intel.com \
    --to=andriy.shevchenko@linux.intel.com \
    --cc=Alexey.Malahov@baikalelectronics.ru \
    --cc=Sergey.Semin@baikalelectronics.ru \
    --cc=abhishekpandit@chromium.org \
    --cc=asierra@xes-inc.com \
    --cc=chromeos-bluetooth-upstreaming@chromium.org \
    --cc=danielwinkler@google.com \
    --cc=fancer.lancer@gmail.com \
    --cc=gregkh@linuxfoundation.org \
    --cc=jslaby@suse.com \
    --cc=linux-bluetooth@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mediatek@lists.infradead.org \
    --cc=linux-serial@vger.kernel.org \
    --cc=lukas@wunner.de \
    --cc=stable@vger.kernel.org \
    --cc=vigneshr@ti.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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.