From: Lukas Wunner <lukas@wunner.de>
To: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Cc: 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>,
Andy Shevchenko <andriy.shevchenko@linux.intel.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 06:11:52 +0200 [thread overview]
Message-ID: <20200702041152.e5csvbodojzwnagx@wunner.de> (raw)
In-Reply-To: <20200701223713.gavale4aramu3xnb@mobilestation>
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;
> 2) Manually call serial8250_do_set_divisor() in the custom set_termios()
> callback.
>
> Just add the uart_update_timeout() and serial8250_do_set_divisor() methods
> invocation into the mtk8250_set_termios() function, which the original commit
> 81bb549fdf14 ("serial: 8250_mtk: support big baud rate") author should have
> done in the first place.
That sound preferable as adding new quirks into core code feels
like a case of midlayer fallacy:
https://blog.ffwll.ch/2016/12/midlayers-once-more-with-feeling.html
Thanks,
Lukas
next prev parent reply other threads:[~2020-07-02 4:12 UTC|newest]
Thread overview: 7+ 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 ` [PATCH v2 1/1] " Daniel Winkler
2020-07-02 7:36 ` Greg Kroah-Hartman
2020-07-01 22:37 ` [PATCH v2 0/1] " Serge Semin
2020-07-02 4:11 ` Lukas Wunner [this message]
2020-07-02 8:46 ` Andy Shevchenko
2020-07-02 7:37 ` Greg Kroah-Hartman
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