linux-kernel - Re: [PATCH] drm: count reaches -1, tested 0

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Date:	Mon, 09 Feb 2009 23:22:31 +0100
From:	Thomas Hellström <thomas@...pmail.org>
To:	Roel Kluin <roel.kluin@...il.com>
CC:	airlied@...ux.ie, dri-devel@...ts.sourceforge.net,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm: count reaches -1, tested 0

Hi!

Roel Kluin wrote:
> With a postfix decrement count will reach -1 rather than 0,
> subsequent tests fail.
>   
This code is about to be abandoned, but if we're going to fix it, 
instead of pushing the problem to then next while loop, what about

while (count && condition)
    count--;

Can you redo the patch based on that?


Thanks,
Thomas

> Signed-off-by: Roel Kluin <roel.kluin@...il.com>
> ---
> diff --git a/drivers/gpu/drm/via/via_dma.c b/drivers/gpu/drm/via/via_dma.c
> index 7a339db..600315c 100644
> --- a/drivers/gpu/drm/via/via_dma.c
> +++ b/drivers/gpu/drm/via/via_dma.c
> @@ -481,9 +481,9 @@ static int via_wait_idle(drm_via_private_t * dev_priv)
>  {
>  	int count = 10000000;
>  
> -	while (!(VIA_READ(VIA_REG_STATUS) & VIA_VR_QUEUE_BUSY) && count--);
> +	while (!(VIA_READ(VIA_REG_STATUS) & VIA_VR_QUEUE_BUSY) && --count);
>  
> -	while (count-- && (VIA_READ(VIA_REG_STATUS) &
> +	while (--count && (VIA_READ(VIA_REG_STATUS) &
>  			   (VIA_CMD_RGTR_BUSY | VIA_2D_ENG_BUSY |
>  			    VIA_3D_ENG_BUSY))) ;
>  	return count;
> @@ -705,7 +705,7 @@ static int via_cmdbuf_size(struct drm_device *dev, void *data, struct drm_file *
>  	switch (d_siz->func) {
>  	case VIA_CMDBUF_SPACE:
>  		while (((tmp_size = via_cmdbuf_space(dev_priv)) < d_siz->size)
> -		       && count--) {
> +		       && --count) {
>  			if (!d_siz->wait) {
>  				break;
>  			}
> @@ -717,7 +717,7 @@ static int via_cmdbuf_size(struct drm_device *dev, void *data, struct drm_file *
>  		break;
>  	case VIA_CMDBUF_LAG:
>  		while (((tmp_size = via_cmdbuf_lag(dev_priv)) > d_siz->size)
> -		       && count--) {
> +		       && --count) {
>  			if (!d_siz->wait) {
>  				break;
>  			}
>
>
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