On Tue, Sep 23, 2008 at 09:31:09AM +0800, Eric Miao wrote: > > Allocating such small buffers using kmalloc seems pretty inefficient. > > At the very least, I would allocate both buffers at once. But quite > > frankly I don't get why you don't just make these buffers part of > > struct max1111_data. This would even make the structure smaller! > > > > I originally place the buffer within "struct max1111_data" but received > a mail from David Brownell suggesting using a kmalloc() buffer, so that > DMA mode will work better with the cache alignment and trailing bytes, > though PIO can just work happily. I don't know the specific reason for > this, honestly. Having cachelines overlap with other data which may be modified during the DMA causes problems on non-cache coherent hardware. It's much safer to ensure that DMA buffers don't share cache lines with anything else.
