This is a note to let you know that I've just added the patch titled

serial: 8250_dw: Revert "Improve clock rate setting"

to the 4.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: serial-8250_dw-revert-improve-clock-rate-setting.patch and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From c14b65feac9ebed649d6fe79c6b6d64d21d0287d Mon Sep 17 00:00:00 2001

From: Andy Shevchenko andriy.shevchenko@linux.intel.com Date: Fri, 19 Jan 2018 18:02:05 +0200 Subject: serial: 8250_dw: Revert "Improve clock rate setting"

From: Andy Shevchenko andriy.shevchenko@linux.intel.com

commit c14b65feac9ebed649d6fe79c6b6d64d21d0287d upstream.

The commit

de9e33bdfa22 ("serial: 8250_dw: Improve clock rate setting")

obviously tries to cure symptoms, and not a root cause.

The root cause is the non-flexible rate calculation inside the corresponding clock driver. What we need is to provide maximum UART divisor value to the clock driver to allow it do the job transparently to the caller.

Since from the initial commit message I have got no clue which clock driver actually needs to be amended, I leave this exercise to the people who know better the case.

Moreover, it seems [1] the fix introduced a regression. And possible even one more [2].

Taking above, revert the commit de9e33bdfa22 for now.

[1]: https://www.spinics.net/lists/linux-serial/msg28872.html [2]: https://github.com/Dunedan/mbp-2016-linux/issues/29#issuecomment-357583782

Fixes: de9e33bdfa22 ("serial: 8250_dw: Improve clock rate setting") Cc: Ed Blake ed.blake@sondrel.com Cc: Heikki Krogerus heikki.krogerus@linux.intel.com Cc: Lukas Wunner lukas@wunner.de Signed-off-by: Andy Shevchenko andriy.shevchenko@linux.intel.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- drivers/tty/serial/8250/8250_dw.c | 30 ++++++++++++------------------ 1 file changed, 12 insertions(+), 18 deletions(-)

--- a/drivers/tty/serial/8250/8250_dw.c +++ b/drivers/tty/serial/8250/8250_dw.c @@ -252,31 +252,25 @@ static void dw8250_set_termios(struct ua struct ktermios *old) { unsigned int baud = tty_termios_baud_rate(termios); - unsigned int target_rate, min_rate, max_rate; struct dw8250_data *d = p->private_data; long rate; - int i, ret; + int ret;

if (IS_ERR(d->clk) || !old) goto out;

- /* Find a clk rate within +/-1.6% of an integer multiple of baudx16 */ - target_rate = baud * 16; - min_rate = target_rate - (target_rate >> 6); - max_rate = target_rate + (target_rate >> 6); - - for (i = 1; i <= UART_DIV_MAX; i++) { - rate = clk_round_rate(d->clk, i * target_rate); - if (rate >= i * min_rate && rate <= i * max_rate) - break; - } - if (i <= UART_DIV_MAX) { - clk_disable_unprepare(d->clk); + clk_disable_unprepare(d->clk); + rate = clk_round_rate(d->clk, baud * 16); + if (rate < 0) + ret = rate; + else if (rate == 0) + ret = -ENOENT; + else ret = clk_set_rate(d->clk, rate); - clk_prepare_enable(d->clk); - if (!ret) - p->uartclk = rate; - } + clk_prepare_enable(d->clk); + + if (!ret) + p->uartclk = rate;

out: p->status &= ~UPSTAT_AUTOCTS;

Patches currently in stable-queue which might be from andriy.shevchenko@linux.intel.com are

queue-4.15/serial-8250_dw-revert-improve-clock-rate-setting.patch