linux-kernel - Re: [PATCH] staging: fbtft: fb_watterott: fix usleep

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Date:   Sun, 1 Nov 2020 12:32:44 +0200
From:   Hassan Shahbazi <hassan.shahbazi@...ia.fi>
To:     Greg KH <greg@...ah.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: fbtft: fb_watterott: fix usleep_range is
 preferred over udelay

On Sun, Nov 01, 2020 at 07:39:48AM +0100, Greg KH wrote:
> On Sun, Nov 01, 2020 at 02:20:10AM +0200, Hassan Shahbazi wrote:
> > Fix the checkpath.pl issue on fb_watterott.c. write_vmem and
> > write_vmem_8bit functions are within non-atomic context and can
> > safely use usleep_range.
> > see Documentation/timers/timers-howto.txt
> > 
> > Signed-off-by: Hassan Shahbazi <hassan@...chat.com>
> > ---
> >  drivers/staging/fbtft/fb_watterott.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/staging/fbtft/fb_watterott.c b/drivers/staging/fbtft/fb_watterott.c
> > index 76b25df376b8..afcc86a17995 100644
> > --- a/drivers/staging/fbtft/fb_watterott.c
> > +++ b/drivers/staging/fbtft/fb_watterott.c
> > @@ -84,7 +84,7 @@ static int write_vmem(struct fbtft_par *par, size_t offset, size_t len)
> >  			par->txbuf.buf, 10 + par->info->fix.line_length);
> >  		if (ret < 0)
> >  			return ret;
> > -		udelay(300);
> > +		usleep_range(300, 310);
> >  	}
> >  
> >  	return 0;
> > @@ -124,7 +124,7 @@ static int write_vmem_8bit(struct fbtft_par *par, size_t offset, size_t len)
> >  			par->txbuf.buf, 10 + par->info->var.xres);
> >  		if (ret < 0)
> >  			return ret;
> > -		udelay(700);
> > +		usleep_range(700, 710);
> 
> How do you know that these ranges are ok?  Are you able to test these
> changes with real hardware?
> 
> thanks,
> 
> greg k-h

No, I don't have the hardware to test with. I just used the current
value as the minimum and added an epsilon to it for the maximum
param.

best, hassan shahbazi