Re: [PATCH] staging: fbtft: fb_watterott: fix usleep_range is preferred over udelay

[Greg KH]

On Sun, Nov 01, 2020 at 12:32:44PM +0200, Hassan Shahbazi wrote:
> 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@xxxxxxxxxxx>
> > > ---
> > >  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.

It's best not to guess about this, sorry, you should have the hardware
to test this type of change.

thanks,

greg k-h