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

Becky Bruce
2008-12-19T18:15:20Z

On Dec 19, 2008, at 11:46 AM, Jeremy Fitzhardinge wrote:

> 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.

Right - in the ppc case, I don't ever need to bounce a lowmem page, so
I wasn't taking that into account. But what you suggest makes sense.

>
>
>> + /* 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.

Yeah, it still needs a bit of clean-up.... I need to scrub for stuff
like this. That loop changed a few times and I hacked it into working
and haven't cleaned it up yet.

Thanks for taking a look! Given how similar the two patches are, it's
pretty clear that we're either both insane, or both headed in the
right direction :)

Anyway, I'm about to turn into a pumpkin - I'll probably be online for
another hour or so sometime this afternoon, and then that's it for me
until after I get back from vacation. My apologies again for
disappearing in the middle of the fun.

Cheers,
-B