[PATCH RFC 087/111] staging: etnaviv: align command stream size to 64 bit

[Russell King - ARM Linux]

On Thu, Apr 02, 2015 at 05:30:29PM +0200, Lucas Stach wrote:
> It is legal for the userspace to pass in a command stream of a size
> aligned to 32 bit, if that is where the last user command ends. The
> kernel then needs to insert a LINK command at the end of the stream,
> which needs to be aligned to 64 bit, so the kernel may insert an
> additional 32bits of padding in the stream. Align the stream size
> to account for that in the size and command stream validator checks.
> 
> Signed-off-by: Lucas Stach <l.stach at pengutronix.de>
> ---
>  drivers/staging/etnaviv/etnaviv_gem_submit.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/staging/etnaviv/etnaviv_gem_submit.c b/drivers/staging/etnaviv/etnaviv_gem_submit.c
> index 7bd4912ab8ad..965096be5219 100644
> --- a/drivers/staging/etnaviv/etnaviv_gem_submit.c
> +++ b/drivers/staging/etnaviv/etnaviv_gem_submit.c
> @@ -377,8 +377,11 @@ int etnaviv_ioctl_gem_submit(struct drm_device *dev, void *data,
>  
>  		/*
>  		 * We must have space to add a LINK command at the end of
> -		 * the command buffer.
> +		 * the command buffer. Align buffer size to the next 64bit
> +		 * quantity, as that's the point where we need to insert the
> +		 * next command.
>  		 */
> +		submit_cmd.size = ALIGN(submit_cmd.size, 8);
>  		max_size = etnaviv_obj->base.size - 8;

I wonder if it's an error if the command size is not a multiple of 8?
I know that the command stream is always aligned to 8 bytes for the 2D
cores, but I don't know about the 3D or VG cores.

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