[PATCH 1/1][SRU][B][D][E][F] UBUNTU: SAUCE: platform/x86: dell-uart-backlight: add retry for get scalar status

[AceLan Kao]

No, it won't impact boot speed, msleep() could be re-schedule.
And yes, it only impacts those machines can't reply
dell_uart_get_scalar_status() in time.

Seth Forshee <seth.forshee at canonical.com> 於 2020年1月9日 週四 上午1:21寫道：
>
> On Wed, Jan 08, 2020 at 03:59:45PM +0800, AceLan Kao wrote:
> > BugLink: https://bugs.launchpad.net/bugs/1858761
> >
> > Found on new platforms that UART require more than 1 second to respond
> > commands in the first 10 seconds after booted.
> > dell_uart_get_scalar_status() is the first command we send to scalar and
> > this command should be more reliable than other commands, and make sure
> > we got correct response from scalar. So, add retry and increase the read
> > timeout to 2 seconds.
> >
> > Signed-off-by: AceLan Kao <acelan.kao at canonical.com>
>
> It looks like this happens during probe, does it affect boot speed?
> Obviously it should only impact a limited set of hw platforms, just
> curious.
>
> Thanks,
> Seth
>
> > ---
> >  drivers/platform/x86/dell-uart-backlight.c | 8 ++++++--
> >  1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/platform/x86/dell-uart-backlight.c b/drivers/platform/x86/dell-uart-backlight.c
> > index 90b28865896a..76e9a60a9388 100644
> > --- a/drivers/platform/x86/dell-uart-backlight.c
> > +++ b/drivers/platform/x86/dell-uart-backlight.c
> > @@ -318,7 +318,7 @@ static int dell_uart_get_scalar_status(struct dell_uart_backlight *dell_pdata)
> >       struct dell_uart_bl_cmd *bl_cmd = &uart_cmd[DELL_UART_GET_SCALAR];
> >       struct uart_8250_port *uart = serial8250_get_port(dell_pdata->line);
> >       int rx_len;
> > -     int status = 0;
> > +     int status = 0, retry = 20;
> >
> >       dell_uart_dump_cmd(__func__, "tx: ", bl_cmd->cmd, bl_cmd->tx_len);
> >
> > @@ -328,7 +328,11 @@ static int dell_uart_get_scalar_status(struct dell_uart_backlight *dell_pdata)
> >       }
> >
> >       dell_uart_write(uart, bl_cmd->cmd, bl_cmd->tx_len);
> > -     rx_len = dell_uart_read(uart, bl_cmd->ret, bl_cmd->rx_len);
> > +     do {
> > +             rx_len = dell_uart_read(uart, bl_cmd->ret, bl_cmd->rx_len);
> > +             if (rx_len == 0)
> > +                     msleep(100);
> > +     } while (rx_len == 0 && --retry);
> >
> >       mutex_unlock(&dell_pdata->brightness_mutex);
> >
> > --
> > 2.17.1
> >
> >
> > --
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> > kernel-team at lists.ubuntu.com
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