Hi Sreeram, On Tue, Sep 10, 2019 at 2:25 AM Sreeram Veluthakkal <srrmvlt@xxxxxxxxx> wrote: > On Mon, Sep 09, 2019 at 10:56:25AM +0100, Greg KH wrote: > > On Sun, Sep 08, 2019 at 08:26:05PM -0500, Sreeram Veluthakkal wrote: > > > This patch fixes the issue: > > > FILE: drivers/staging/fbtft/fb_agm1264k-fl.c:88: > > > CHECK: usleep_range is preferred over udelay; see Documentation/timers/timers-howto.rst > > > + udelay(20); > > > > > > Signed-off-by: Sreeram Veluthakkal <srrmvlt@xxxxxxxxx> Thanks for your patch! > > > --- a/drivers/staging/fbtft/fb_agm1264k-fl.c > > > +++ b/drivers/staging/fbtft/fb_agm1264k-fl.c > > > @@ -85,7 +85,7 @@ static void reset(struct fbtft_par *par) > > > dev_dbg(par->info->device, "%s()\n", __func__); > > > > > > gpiod_set_value(par->gpio.reset, 0); > > > - udelay(20); > > > + usleep_range(20, 40); > > > > Is it "safe" to wait 40? This kind of change you can only do if you > > know this is correct. Have you tested this with hardware? > > > > thanks, > > > > greg k-h > > Hi Greg, No I haven't tested it, I don't have the hw. I dug depeer in to the usleep_range > > https://github.com/torvalds/linux/blob/master/kernel/time/timer.c#L1993 > u64 delta = (u64)(max - min) * NSEC_PER_USEC; > > * The @delta argument gives the kernel the freedom to schedule the > * actual wakeup to a time that is both power and performance friendly. > * The kernel give the normal best effort behavior for "@expires+@delta", > * but may decide to fire the timer earlier, but no earlier than @expires. > > My understanding is that keeping delta 0 (min=max=20) would be equivalent. > I can revise the patch to usleep_range(20, 20) or usleep_range(20, 21) for a 1 usec delta. > What do you suggest? Please read the comment above the line you're referring to: * In non-atomic context where the exact wakeup time is flexible, use * usleep_range() instead of udelay(). The sleep improves responsiveness * by avoiding the CPU-hogging busy-wait of udelay(), and the range reduces * power usage by allowing hrtimers to take advantage of an already- * scheduled interrupt instead of scheduling a new one just for this sleep. Is this function always called in non-atomic context? If it may be called in atomic context, replacing the udelay() call by a usleep*() call will break the driver. See also "the first and most important question" in Documentation/timers/timers-howto.rst, as referred to by the checkpatch.pl message. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx 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 _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
