On Tue, Mar 08, 2011 at 09:52:54PM +0100, Thomas Hellstrom wrote:
Hi, Konrad,
Is passing a struct device to the DMA api really *strictly* necessary?
Soo.. it seems it is on PowerPC, which I sadly didn't check for, does require this.
I'd like to avoid that at all cost, since we don't want pages that are backing buffer objects (coherent pages) to be associated with a specific device.
The reason for this is that we probably soon will want to move ttm buffer objects between devices, and that should ideally be a simple operation: If the memory type the buffer object currently resides in is not shared between two devices, then move it out to system memory and change its struct bo_device pointer.
I was thinking about this a bit after I found that the PowerPC requires the 'struct dev'. But I got a question first, what do you with pages that were allocated to a device that can do 64-bit DMA and then move it to a device than can 32-bit DMA? Obviously the 32-bit card would set the TTM_PAGE_FLAG_DMA32 flag, but the 64-bit would not. What is the process then? Allocate a new page from the 32-bit device and then copy over the page from the 64-bit TTM and put the 64-bit TTM page?
If pages are associated with a specific device, this will become much harder. Basically we need to change backing pages and copy all
what if you track it. Right now you need to track two things: 'struct page *' and 'dma_addr_t'. What if you had also to track 'struct dev *' with the page in question? Something like this:
diff --git a/include/drm/ttm/ttm_bo_driver.h b/include/drm/ttm/ttm_bo_driver.h index efed082..1986761 100644 --- a/include/drm/ttm/ttm_bo_driver.h +++ b/include/drm/ttm/ttm_bo_driver.h @@ -158,9 +158,14 @@ enum ttm_caching_state { * memory. */
+struct ttm_tt_page { + struct page *page; + dma_addr_t *dma_addr; + struct dev *dev; +} struct ttm_tt { struct page *dummy_read_page; - struct page **pages; + struct ttm_tt_page **pages; long first_himem_page; long last_lomem_page; uint32_t page_flags; @@ -176,7 +181,6 @@ struct ttm_tt { tt_unbound, tt_unpopulated, } state; - dma_addr_t *dma_address; };
#define TTM_MEMTYPE_FLAG_FIXED (1 << 0) /* Fixed (on-card) PCI memory */
could do it. And when you pass the 'page' to the other TTM, it is just the matter of passing in the 'struct ttm_tt_page' now.