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

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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
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)





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