On Mon, May 11, 2015 at 09:27:35PM +0200, Martin Sperl wrote: > > On 11.05.2015, at 20:00, Mark Brown <broonie@xxxxxxxxxx> wrote: > > No, it's supposed to be usable for PIO too - it can keep logic simpler. > but only slightly - it is a simple > (xfer->tx_buf) ? xfer->tx_buf[i] : 0 > so I do not see a huge difference. People can make the logic more complex than that. > > Indeed, just having a page that gets reused would be better. I'm hoping > > that someone who needs this will get around to optimizing it at some > > point. > I could possibly look into that, but it goes against the point you > made above about PIO. > Either we allocate the memory completely and make it work for PIO. > Or we only create a scatter/gather list of the same page and leave > tx_buf == NULL. We can tell if it's a DMA transfer - if it's a DMA transfer then using anything except the SG list is a bit dodgy anyway since you're not really supposed to have the CPU look at anything that's mapped for the device (though it's generally fine if the device never actually DMAs). > So unless we have a separate flag to say we only need it for DMA, > then we have to keep the the current logic with allocation or we break > other drivers. We essentially have that; anything looking at a DMA mapped transfer had better cope.
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