* [PATCH] FBTFT: fb_agm1264k: usleep_range is preferred over udelay
@ 2019-09-09 1:26 Sreeram Veluthakkal
2019-09-09 9:56 ` Greg KH
0 siblings, 1 reply; 4+ messages in thread
From: Sreeram Veluthakkal @ 2019-09-09 1:26 UTC (permalink / raw)
To: gregkh
Cc: devel, linux-fbdev, nishadkamdar, linux-kernel, dri-devel,
payal.s.kshirsagar.98, Sreeram Veluthakkal
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@gmail.com>
---
drivers/staging/fbtft/fb_agm1264k-fl.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/staging/fbtft/fb_agm1264k-fl.c b/drivers/staging/fbtft/fb_agm1264k-fl.c
index eeeeec97ad27..2dece71fd3b5 100644
--- 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);
gpiod_set_value(par->gpio.reset, 1);
mdelay(120);
}
--
2.17.1
_______________________________________________
devel mailing list
devel@linuxdriverproject.org
http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] FBTFT: fb_agm1264k: usleep_range is preferred over udelay
2019-09-09 1:26 [PATCH] FBTFT: fb_agm1264k: usleep_range is preferred over udelay Sreeram Veluthakkal
@ 2019-09-09 9:56 ` Greg KH
2019-09-09 11:50 ` Sreeram Veluthakkal
0 siblings, 1 reply; 4+ messages in thread
From: Greg KH @ 2019-09-09 9:56 UTC (permalink / raw)
To: Sreeram Veluthakkal
Cc: devel, linux-fbdev, nishadkamdar, linux-kernel, dri-devel,
payal.s.kshirsagar.98
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@gmail.com>
> ---
> drivers/staging/fbtft/fb_agm1264k-fl.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/staging/fbtft/fb_agm1264k-fl.c b/drivers/staging/fbtft/fb_agm1264k-fl.c
> index eeeeec97ad27..2dece71fd3b5 100644
> --- 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
_______________________________________________
devel mailing list
devel@linuxdriverproject.org
http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] FBTFT: fb_agm1264k: usleep_range is preferred over udelay
2019-09-09 9:56 ` Greg KH
@ 2019-09-09 11:50 ` Sreeram Veluthakkal
2019-09-10 7:59 ` Geert Uytterhoeven
0 siblings, 1 reply; 4+ messages in thread
From: Sreeram Veluthakkal @ 2019-09-09 11:50 UTC (permalink / raw)
To: Greg KH
Cc: devel, linux-fbdev, nishadkamdar, linux-kernel, dri-devel,
payal.s.kshirsagar.98
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@gmail.com>
> > ---
> > drivers/staging/fbtft/fb_agm1264k-fl.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/staging/fbtft/fb_agm1264k-fl.c b/drivers/staging/fbtft/fb_agm1264k-fl.c
> > index eeeeec97ad27..2dece71fd3b5 100644
> > --- 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?
thanks,
Sreeram
_______________________________________________
devel mailing list
devel@linuxdriverproject.org
http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] FBTFT: fb_agm1264k: usleep_range is preferred over udelay
2019-09-09 11:50 ` Sreeram Veluthakkal
@ 2019-09-10 7:59 ` Geert Uytterhoeven
0 siblings, 0 replies; 4+ messages in thread
From: Geert Uytterhoeven @ 2019-09-10 7:59 UTC (permalink / raw)
To: Sreeram Veluthakkal
Cc: driverdevel, Linux Fbdev development list, nishadkamdar, Greg KH,
Linux Kernel Mailing List, DRI Development,
payal.s.kshirsagar.98
Hi Sreeram,
On Tue, Sep 10, 2019 at 2:25 AM Sreeram Veluthakkal <srrmvlt@gmail.com> 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@gmail.com>
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@linux-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
_______________________________________________
devel mailing list
devel@linuxdriverproject.org
http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2019-09-10 8:00 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-09-09 1:26 [PATCH] FBTFT: fb_agm1264k: usleep_range is preferred over udelay Sreeram Veluthakkal
2019-09-09 9:56 ` Greg KH
2019-09-09 11:50 ` Sreeram Veluthakkal
2019-09-10 7:59 ` Geert Uytterhoeven
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).