Re: [PATCH 07/11] swiotlb: Add support for systems with highmem

Jeremy Fitzhardinge
2008-12-19T17:46:40Z

Becky Bruce wrote:
> On highmem systems, the original dma buffer might not
> have a virtual mapping - we need to kmap it in to perform
> the bounce. Extract the code that does the actual
> copy into a function that does the kmap if highmem
> is enabled, and defaults to the normal swiotlb memcpy
> if not.
>
> Signed-off-by: Becky Bruce <beckyb@kernel.crashing.org>
> ---
> lib/swiotlb.c | 53 +++++++++++++++++++++++++++++++++++++++++++++--------
> 1 files changed, 45 insertions(+), 8 deletions(-)
>
> diff --git a/lib/swiotlb.c b/lib/swiotlb.c
> index e9d5bf6..ab5d3d7 100644
> --- a/lib/swiotlb.c
> +++ b/lib/swiotlb.c
> @@ -14,6 +14,7 @@
> * 04/07/.. ak Better overflow handling. Assorted fixes.
> * 05/09/10 linville Add support for syncing ranges, support syncing for
> * DMA_BIDIRECTIONAL mappings, miscellaneous cleanup.
> + * 08/12/11 beckyb Add highmem support
> */
>
> #include <linux/cache.h>
> @@ -24,6 +25,7 @@
> #include <linux/string.h>
> #include <linux/types.h>
> #include <linux/ctype.h>
> +#include <linux/highmem.h>
>
> #include <asm/io.h>
> #include <asm/dma.h>
> @@ -306,6 +308,45 @@ static int is_swiotlb_buffer(char *addr)
> }
>
> /*
> + * Bounce: copy the swiotlb buffer back to the original dma location
> + */
> +void swiotlb_bounce(phys_addr_t phys, char *dma_addr, size_t size,
> + enum dma_data_direction dir)
> +{
> +#ifdef CONFIG_HIGHMEM
>

Rather than using #ifdef CONFIG_HIGHMEM, I think it would be better to
use something like:

if (PageHighMem(phys_to_page(phys))) {
/* handle high page */
} else {
/* simple path */
}

This will still exclude all the highmem code on non-highmem systems, and
will use the fast-path for lowmem pages too.

> + /* The buffer may not have a mapping. Map it in and copy */
> + unsigned int offset = ((unsigned long)phys &
> + ((1 << PAGE_SHIFT) - 1));
> + char *buffer;
> + unsigned int sz = 0;
> + unsigned long flags;
> +
> + while (size) {
> + sz = ((PAGE_SIZE - offset) > size) ? size :
> + PAGE_SIZE - offset;
>
sz = min(size, PAGE_SIZE - offset)?
> + local_irq_save(flags);
> + buffer = kmap_atomic(pfn_to_page(phys >> PAGE_SHIFT),
>
phys_to_page() does this for you.
> + KM_BOUNCE_READ);
> + if (dir == DMA_TO_DEVICE)
> + memcpy(dma_addr, buffer + offset, sz);
> + else
> + memcpy(buffer + offset, dma_addr, sz);
> + kunmap_atomic(buffer, KM_BOUNCE_READ);
> + local_irq_restore(flags);
> + size -= sz;
> + phys += sz;
> + dma_addr += sz;
> + offset = 0;
> + }
> +#else
> + if (dir == DMA_TO_DEVICE)
> + memcpy(dma_addr, phys_to_virt(phys), size);
> + else
> + memcpy(phys_to_virt(phys), dma_addr, size);
> +#endif
> +}
>

J