linux-kernel - Re: [PATCH 4/4] serial: 8250_dw: Rework ->serial

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Message-ID: <CAHp75VdsTjbEwocx4DAhMBM6nwKhuL3xgaJeZhV=ZhBPz3pdRw@mail.gmail.com>
Date:   Wed, 29 Jun 2022 11:51:13 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc:     "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] serial: 8250_dw: Rework ->serial_out() LCR write
 retry logic

On Wed, Jun 29, 2022 at 11:40 AM Ilpo Järvinen
<ilpo.jarvinen@...ux.intel.com> wrote:
> On Wed, 29 Jun 2022, Andy Shevchenko wrote:
> > On Wed, Jun 29, 2022 at 10:47 AM Ilpo Järvinen
> > <ilpo.jarvinen@...ux.intel.com> wrote:
> > > On Tue, 28 Jun 2022, Andy Shevchenko wrote:

...

> > > Eh, are you suggesting I should do write as a side-effect inside one of
> > > the iopoll.h macros? Because those available seem to only read?
> > >
> > > Or should I create another macro there which writes too?
> >
> > It seems to me that it would be a macro on top of iopoll's one which
> > will take an op read and op write arguments depending on the case.
>
> The thing is those iopoll macros don't return until the timeout is
> exhausted

It returns when the condition is true (in your case verify_lcr is OK).

> so I don't think I can reuse them easily for this task ("on top
> of iopoll's one")? That is, w/o some major side-effect hack (which is
> IMHO a no-go).

Basically what we need is a write-read type of polling.

With your current approach I don't like that retries assignment is
duplicated several times and decrement happens in the callee. What I'm
trying to suggest is to research alternatives.

-- 
With Best Regards,
Andy Shevchenko