Hi Christoph, On 2017/8/29 1:48, Christoph Hellwig wrote:
Hi all, any idea why the mmc driver defaults to bouncing highmem pages if the device doesn't have a DMA mask? highmem is defined different on different architectures or even based on config options, so it seems like a very odd choice.
Not sure why mmc stack defaults to use BLK_BOUNCE_HIGH as it seems that it has been there when mmc was added into linux. I *guess* this is a copy-and-paste from other block drivers, especially see drivers/memstick/core/ms_block.c which does actual the same thing. And that raises another question that if mmc stack doesn't defaults to boucing highmem pages but host drivers don't provide DMA mask either, so what should we use for saftly limiting bouncing for DMA capable?
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