Re: [PATCH v3] serial: sh-sci: Stop dmaengine transfer in sci_stop_tx()

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Jun 10, 2021 at 08:58:04AM +0200, Geert Uytterhoeven wrote:
> Hi Shimoda-san,
> 
> On Thu, Jun 10, 2021 at 2:50 AM Yoshihiro Shimoda
> <yoshihiro.shimoda.uh@renesas.com> wrote:
> > > From: Geert Uytterhoeven, Sent: Thursday, June 10, 2021 12:30 AM
> > > On Wed, Jun 9, 2021 at 5:09 PM Sergei Shtylyov
> > > <sergei.shtylyov@gmail.com> wrote:
> > > > On 6/9/21 4:49 AM, Yoshihiro Shimoda wrote:
> > > > > Stop dmaengine transfer in sci_stop_tx(). Otherwise, the following
> > > > > message is possible output when system enters suspend and while
> > > > > transferring data, because clearing TIE bit in SCSCR is not able to
> > > > > stop any dmaengine transfer.
> > > > >
> > > > >     sh-sci e6550000.serial: ttySC1: Unable to drain transmitter
> > > > >
> > > > > Note that this patch uses dmaengine_terminate_async() so that
> > > > > we can apply this patch into longterm kernel v4.9.x or later.
> > > > >
> > > > > Fixes: 73a19e4c0301 ("serial: sh-sci: Add DMA support.")
> > > > > Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
> > > > > ---
> > > > >
> > > > >  drivers/tty/serial/sh-sci.c | 8 ++++++++
> > > > >  1 file changed, 8 insertions(+)
> > > > >
> > > > > diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
> > > > > index 4baf1316ea72..2d5487bf6855 100644
> > > > > --- a/drivers/tty/serial/sh-sci.c
> > > > > +++ b/drivers/tty/serial/sh-sci.c
> > > > > @@ -610,6 +610,14 @@ static void sci_stop_tx(struct uart_port *port)
> > > > >       ctrl &= ~SCSCR_TIE;
> > > > >
> > > > >       serial_port_out(port, SCSCR, ctrl);
> > > > > +
> > > > > +#ifdef CONFIG_SERIAL_SH_SCI_DMA
> > > >
> > > >    Why not use IS_ENABLED() instead? Gets rid of #ifdef. :-)
> > > >
> > > > > +     if (to_sci_port(port)->chan_tx &&
> > > > > +         !dma_submit_error(to_sci_port(port)->cookie_tx)) {
> > > > > +             dmaengine_terminate_async(to_sci_port(port)->chan_tx);
> > > > > +             to_sci_port(port)->cookie_tx = -EINVAL;
> > >
> > > Because chan_tx and cookie_tx do not exist if CONFIG_SERIAL_SH_SCI_DMA
> > > is disabled.
> >
> > This is a nit though, chan_tx always exists.
> 
> I stand corrected, only cookie_tx depends on CONFIG_SERIAL_SH_SCI_DMA.
> 
> > > Yes, that's why all the DMA code in this driver (.c file) is protected by
> > > #ifdef CONFIG_SERIAL_SH_SCI_DMA.
> >
> > I'm thinking we have to remove #ifdef from sh-sci.c file at first...
> 
> While I don't disagree that would be worthwhile, do we really need
> to refactor a driver first, before a fix that follows the existing
> driver style can be applied (and backported)?

No we do not.  Sorry if this usage is already in the driver, might as
well keep it there, I thought this was an exception and was being added
for the first time here.

thanks,

greg k-h