Re: [PATCH] drm/ast: astdp: fix pre-op vs post-op bug

[Thomas Zimmermann]

Hi

Am 09.08.24 um 19:06 schrieb Dan Carpenter:
> On Fri, Aug 09, 2024 at 04:43:51PM +0300, Jani Nikula wrote:
> > On Fri, 09 Aug 2024, Thomas Zimmermann <tzimmermann@xxxxxxx> wrote:
> > > Hi,
> > >
> > > thanks a lot for the bugfix.
> > >
> > > Am 09.08.24 um 14:33 schrieb Dan Carpenter:
> > > > The test for "Link training failed" expect the loop to exit with "i"
> > > > set to zero but it exits when "i" is set to -1.  Change this from a
> > > > post-op to a pre-op so that it exits with "i" set to zero.  This
> > > > changes the number of iterations from 10 to 9 but probably that's
> > > > okay.
> > > Yes, that's ok.
> > >
> > > > Fixes: 2281475168d2 ("drm/ast: astdp: Perform link training during atomic_enable")
> > > > Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> > > > ---
> > > >    drivers/gpu/drm/ast/ast_dp.c | 2 +-
> > > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/ast/ast_dp.c b/drivers/gpu/drm/ast/ast_dp.c
> > > > index 5d07678b502c..4329ab680f62 100644
> > > > --- a/drivers/gpu/drm/ast/ast_dp.c
> > > > +++ b/drivers/gpu/drm/ast/ast_dp.c
> > > > @@ -148,7 +148,7 @@ void ast_dp_link_training(struct ast_device *ast)
> > > >    	struct drm_device *dev = &ast->base;
> > > >    	unsigned int i = 10;
> > > >    
> > > > -	while (i--) {
> > > > +	while (--i) {
> > > If this loop ever starts with i = 0, it would break again. Can we use
> > >
> > > while (i) {
> > >     --i;
> > >      ...
> > > }
> > >
> > > instead?
> > FWIW, I personally *always* use for loops when there isn't a compelling
> > reason to do otherwise. You know at a glance that
> >
> > 	for (i = 0; i < N; i++)
> >
> > gets run N times and what i is going to be afterwards.
> >
> > Sure, you may have to restructure other things, but I think it's almost
> > always worth it.
> A for statement works here.  I need to resend the patch anyway because
> the if (i) msleep() code doesn't make sense now.

Why? The loop counts downwards and does not wait if the final iteration 
(i == 0) fails.

Personally, I prefer while for counting downwards. But if you do the for 
loop as mentioned, you have to adapt the loop body.

Best regards
Thomas

> regards,
> dan carpenter

--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
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