On Mon, Dec 03, 2018 at 11:56:11AM +0000, John Garry wrote: > On 01/12/2018 16:36, Christoph Hellwig wrote: >> On Fri, Nov 30, 2018 at 07:39:50PM +0000, Robin Murphy wrote: >>> I was assuming the point was to also add something like >>> >>> default 131072 if HNS_ENET >>> >>> so that DMA debug doesn't require too much thought from the user. If they >>> still have to notice the overflow message and empirically figure out a >>> value that does work, rebuilding the kernel each time is far less >>> convenient than simply adding "dma_debug_entries=..." to their kernel >>> command line and rebooting, which they can do today. If they do already >>> know up-front that the default will need overriding and what the >>> appropriate value is, then the command line still seems seems just as >>> convenient. >> >> I'm not so fond of random drivers changing the defaults. My idea >> was rather to have the config option so that the defconfig files for >> the Hisilicon SOCs with this hardware could select a larger number >> without making a total mess of the kernel configuration. >> >> If we really have to we could do different defaults, but I'd still >> much rather do this on a arch/platform basis than specific drivers. > > As I understand, some drivers could even use much more than this (131072), > to such a point where I can't imagine that we would want to set an arch > default to support them. For this HNS_ENET case, it is arm64 specific so it > would be an arch defconfig.
But I'm not sure we could always do the right thing for everyone. I think we might be better of trying to just dynamically allocate entries when we run out of them instead of coming up with a perfect number.
