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