Re: [PATCH v3 1/3] serial: sb1250-duart: Fix console message clobbering at channel resets

[Florian Fainelli <f.fainelli@gmail.com>]

On 8/6/26 03:54, Maciej W. Rozycki wrote:
> Ensure any characters outstanding have been sent before issuing channel
> resets so as to prevent messages issued to the bootconsole from getting
> clobbered.
> 
> Contrary to device documentation at the time the transmitter empty bit
> is set only the transmit FIFO has been drained and there is still data
> outstanding in the transmitter shift register, so wait an extra amount
> of time for that register to drain too.  This also prevents subsequent
> messages produced to the console from getting clobbered, owing to what
> seems a transmitter synchronisation issue.
> 
> When called from sbd_serial_console_init() it is too early for fsleep()
> to work and even before lpj has been calculated, and therefore neither
> udelay() works.  Therefore delay by hand, observing that roughly 170
> iterations over an Input Port Register read are sufficient for the
> transmitter to drain with the BCM1250 SoC clocked at 800MHz, so using
> 2048 iterations should give enough margin including in particular for
> the faster BCM1480 SoC clocked at 1GHz.
> 
> Fixes: b45d52797432 ("sb1250-duart.c: SB1250 DUART serial support")
> Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
> Cc: stable@vger.kernel.org # v2.6.23+

Tested-by: Florian Fainelli <f.fainelli@gmail.com>
-- 
Florian