Re: [PATCH v2 19/29] drm/xe: Add GPUSVM devic memory copy vfunc functions

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On Tue, 2024-10-15 at 20:25 -0700, Matthew Brost wrote:
> Add GPUSVM devic memory copy vfunc functions and connect to migration

s/devic/device 
> 

> layer.
> 
> v2:
>  - Allow NULL device pages in xe_svm_copy
>  - Use new drm_gpusvm_devmem_ops
> 
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
>  drivers/gpu/drm/xe/xe_svm.c | 150
> ++++++++++++++++++++++++++++++++++++
>  1 file changed, 150 insertions(+)
> 
> diff --git a/drivers/gpu/drm/xe/xe_svm.c
> b/drivers/gpu/drm/xe/xe_svm.c
> index 22e6341117bd..b33fd42d035b 100644
> --- a/drivers/gpu/drm/xe/xe_svm.c
> +++ b/drivers/gpu/drm/xe/xe_svm.c
> @@ -6,6 +6,7 @@
>  #include "drm_gpusvm.h"
>  
>  #include "xe_gt_tlb_invalidation.h"
> +#include "xe_migrate.h"
>  #include "xe_pt.h"
>  #include "xe_svm.h"
>  #include "xe_vm.h"
> @@ -269,6 +270,155 @@ static void
> xe_svm_garbage_collector_work_func(struct work_struct *w)
>  	up_write(&vm->lock);
>  }
>  
> +static struct xe_mem_region *page_to_mr(struct page *page)
> +{
> +	return container_of(page->pgmap, struct xe_mem_region,
> pagemap);
> +}
> +
> +static struct xe_tile *mr_to_tile(struct xe_mem_region *mr)
> +{
> +	return container_of(mr, struct xe_tile, mem.vram);
> +}
> +
> +static u64 xe_mem_region_page_to_dpa(struct xe_mem_region *mr,
> +				     struct page *page)
> +{
> +	u64 dpa;
> +	struct xe_tile *tile = mr_to_tile(mr);
> +	u64 pfn = page_to_pfn(page);
> +	u64 offset;
> +
> +	xe_tile_assert(tile, is_device_private_page(page));
> +	xe_tile_assert(tile, (pfn << PAGE_SHIFT) >= mr->hpa_base);
> +
> +	offset = (pfn << PAGE_SHIFT) - mr->hpa_base;
> +	dpa = mr->dpa_base + offset;
> +
> +	return dpa;
> +}
> +
> +enum xe_svm_copy_dir {
> +	XE_SVM_COPY_TO_VRAM,
> +	XE_SVM_COPY_TO_SRAM,
> +};
> +
> +static int xe_svm_copy(struct page **pages, dma_addr_t *dma_addr,
> +		       unsigned long npages, const enum
> xe_svm_copy_dir dir)
> +{
> +	struct xe_mem_region *mr = NULL;
> +	struct xe_tile *tile;
> +	struct dma_fence *fence = NULL;
> +	unsigned long i;
> +#define VRAM_ADDR_INVALID	~0x0ull
> +	u64 vram_addr = VRAM_ADDR_INVALID;
> +	int err = 0, pos = 0;
> +	bool sram = dir == XE_SVM_COPY_TO_SRAM;
> +
> +	for (i = 0; i < npages; ++i) {
> +		struct page *spage = pages[i];
> +		struct dma_fence *__fence;
> +		u64 __vram_addr;
> +		bool match = false, chunk, last;
> +
> +		chunk = (i - pos) == (SZ_2M / PAGE_SIZE);
> +		last = (i + 1) == npages;
> +
> +		if (!dma_addr[i] && vram_addr == VRAM_ADDR_INVALID)
> +			continue;
> +
> +		if (!mr && spage) {
> +			mr = page_to_mr(spage);
> +			tile = mr_to_tile(mr);
> +		}
> +
> +		if (dma_addr[i] && spage) {
> +			__vram_addr = xe_mem_region_page_to_dpa(mr,
> spage);
> +			if (vram_addr == VRAM_ADDR_INVALID) {
> +				vram_addr = __vram_addr;
> +				pos = i;
> +			}
> +
> +			match = vram_addr + PAGE_SIZE * (i - pos) ==
> __vram_addr;
> +		}
> +
> +		if (!match || chunk || last) {
> +			int incr = (match && last) ? 1 : 0;
> +
> +			if (vram_addr != VRAM_ADDR_INVALID) {
> +				if (sram)
> +					__fence =
> xe_migrate_from_vram(tile->migrate,
> +								    
>    i - pos + incr,
> +								    
>    vram_addr,
> +								    
>    dma_addr + pos);
> +				else
> +					__fence =
> xe_migrate_to_vram(tile->migrate,
> +								    
> i - pos + incr,
> +								    
> dma_addr + pos,
> +								    
> vram_addr);
> +				if (IS_ERR(__fence)) {
> +					err = PTR_ERR(__fence);
> +					goto err_out;
> +				}
> +
> +				dma_fence_put(fence);
> +				fence = __fence;
> +			}
> +
> +			if (dma_addr[i] && spage) {
> +				vram_addr = __vram_addr;
> +				pos = i;
> +			} else {
> +				vram_addr = VRAM_ADDR_INVALID;
> +			}
> +
> +			if (!match && last && dma_addr[i] && spage)
> {
> +				if (sram)
> +					__fence =
> xe_migrate_from_vram(tile->migrate, 1,
> +								    
>    vram_addr,
> +								    
>    dma_addr + pos);
> +				else
> +					__fence =
> xe_migrate_to_vram(tile->migrate, 1,
> +								    
> dma_addr + pos,
> +								    
> vram_addr);
> +				if (IS_ERR(__fence)) {
> +					err = PTR_ERR(__fence);
> +					goto err_out;
> +				}
> +
> +				dma_fence_put(fence);
> +				fence = __fence;
> +			}

I think the flow in this function is a bit hard to follow. Could it
perhaps be simplified? If not, perhaps add a comment to the function
what it expects from the input arguments and the possible corner cases
that complicates it?


> +		}
> +	}
> +
> +err_out:
> +	if (fence) {
> +		dma_fence_wait(fence, false);
> +		dma_fence_put(fence);
> +	}
> +
> +	return err;
> +#undef VRAM_ADDR_INVALID
> +}
> +
> +static int xe_svm_copy_to_devmem(struct page **pages, dma_addr_t
> *dma_addr,
> +				 unsigned long npages)
> +{
> +	return xe_svm_copy(pages, dma_addr, npages,
> XE_SVM_COPY_TO_VRAM);
> +}
> +
> +static int xe_svm_copy_to_ram(struct page **pages, dma_addr_t
> *dma_addr,
> +			      unsigned long npages)
> +{
> +	return xe_svm_copy(pages, dma_addr, npages,
> XE_SVM_COPY_TO_SRAM);
> +}
> +
> +__maybe_unused

Is this __maybe_unused to be removed in a follow-up patch? If so could
you add a comment stating that?

> +static const struct drm_gpusvm_devmem_ops gpusvm_devmem_ops = {
> +	.copy_to_devmem = xe_svm_copy_to_devmem,
> +	.copy_to_ram = xe_svm_copy_to_ram,
> +};
> +
>  static const struct drm_gpusvm_ops gpusvm_ops = {
>  	.range_alloc = xe_svm_range_alloc,
>  	.range_free = xe_svm_range_free,

Thanks,
Thomas