Re: [PATCH 2/3] drm/etnaviv: Map and unmap the GPU VA range with respect to its user size

[Sui Jingfeng]

Hi,

On 2024/10/7 18:17, Lucas Stach wrote:
> >   
> > @@ -104,21 +108,7 @@ static int etnaviv_iommu_map(struct etnaviv_iommu_context *context, u32 iova,
> >   static void etnaviv_iommu_unmap(struct etnaviv_iommu_context *context, u32 iova,
> >   				struct sg_table *sgt, unsigned len)
> >   {
> > -	struct scatterlist *sg;
> > -	unsigned int da = iova;
> > -	int i;
> > -
> > -	for_each_sgtable_dma_sg(sgt, sg, i) {
> > -		size_t bytes = sg_dma_len(sg) + sg->offset;


Why the length of a single SG segment is `sg_dma_len(sg) + sg->offset` here?


> > -		etnaviv_context_unmap(context, da, bytes);
> > -
> > -		VERB("unmap[%d]: %08x(%zx)", i, iova, bytes);
> > -
> > -		BUG_ON(!PAGE_ALIGNED(bytes));
> > -
> > -		da += bytes;
> > -	}
> > +	etnaviv_context_unmap(context, iova, len);
> This drops some sanity checks, but I have only ever seen them fire when
> we had other kernel memory corruption issues, so I'm fine with the
> simplification you did here.


Isn't that 'sg_dma_len(sg)' itself is the length of its backing memory ?


> Regards,
> Lucas

--
Best regards,
Sui