linux-kernel - Re: [PATCH v10] staging: fbtft: add tearing signal detect

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Date:   Thu, 28 Jan 2021 10:42:54 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Kari Argillander <kari.argillander@...il.com>
Cc:     carlis <zhangxuezhi3@...il.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Colin King <colin.king@...onical.com>,
        oliver.graute@...oconnector.com, zhangxuezhi1@...ong.com,
        mh12gx2825@...il.com, Stefano Brivio <sbrivio@...hat.com>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        driverdevel <devel@...verdev.osuosl.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v10] staging: fbtft: add tearing signal detect

Hi Kari,

On Thu, Jan 28, 2021 at 7:53 AM Kari Argillander
<kari.argillander@...il.com> wrote:
> On Thu, Jan 28, 2021 at 09:42:58AM +0800, carlis wrote:
> > On Thu, 28 Jan 2021 00:32:22 +0200
> > Kari Argillander <kari.argillander@...il.com> wrote:
> > > >  #include "fbtft.h"
> > > >
> > > >  #define DRVNAME "fb_st7789v"
> > > > @@ -66,6 +69,32 @@ enum st7789v_command {
> > > >  #define MADCTL_MX BIT(6) /* bitmask for column address order */
> > > >  #define MADCTL_MY BIT(7) /* bitmask for page address order */
> > > >
> > > > +#define SPI_PANEL_TE_TIMEOUT     400 /* msecs */
> > > > +static struct mutex te_mutex;/* mutex for set te gpio irq status
> > > > */
> > >
> > > Space after ;
> > hi, i have fix it in the patch v11
> > >
>
> Yeah sorry. I accidentally review wrong patch. But mostly stuff are
> still relevant.
>
> > > > @@ -82,6 +111,33 @@ enum st7789v_command {
> > > >   */
> > > >  static int init_display(struct fbtft_par *par)
> > > >  {
> > > > + int rc;
> > > > + struct device *dev = par->info->device;
> > > > +
> > > > + par->gpio.te = devm_gpiod_get_index_optional(dev, "te", 0,
> > > > GPIOD_IN);
> > > > + if (IS_ERR(par->gpio.te)) {
> > > > +         rc = PTR_ERR(par->gpio.te);
> > > > +         dev_err(par->info->device, "Failed to request te
> > > > gpio: %d\n", rc);
> > > > +         return rc;
> > > > + }
> > >
> > > You request with optinal and you still want to error out? We could
> > > just continue and not care about that error. User will be happier if
> > > device still works somehow.

devm_gpiod_get_index_optional() returns NULL, not an error, if the
GPIO is not found.  So if IS_ERR() is the right check.

And checks for -EPROBE_DEFER can be handled automatically
by using dev_err_probe() instead of dev_err().

> > You mean i just delete this dev_err print ?!
> > like this:
> >       par->gpio.te = devm_gpiod_get_index_optional(dev, "te",
> > 0,GPIOD_IN);
> >         if (IS_ERR(par->gpio.te))
> >               return PTR_ERR(par->gpio.te);
>
> Not exactly. I'm suggesting something like this.
>
> if (IS_ERR(par->gpio.te) == -EPROBE_DEFER) {
>         return -EPROBE_DEFER;
>
> if (IS_ERR(par->gpio.te))
>         par-gpio.te = NULL;
>
> This like beginning of your patch series but the difference is that if
> EPROBE_DEFER then we will try again later. Any other error and we will
> just ignore TE gpio. But this is up to you what you want to do. To me
> this just seems place where this kind of logic can work.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds