On Mon, Jul 20, 2015 at 09:04:05AM +0200, Alexander Stein wrote: > On Thursday 16 July 2015 20:06:57, Mark Brown wrote:
Please fix your mailer to word wrap within paragraphs for legibility. > > The expectation here is that we should either be using no or a flat > > cache here or (if we're using rbtree) providing register defaults to > > ensure that we never do allocations in the spinlock. The rbtree code is > > written on the assumption that we only have to be faster than reading > > from a serial bus so I'd be worried about it not behaving at all nicely > > in a spinlock even ignoring this issue. > AFAICS even a flat cache seems also only be usefull when providing > defaults, no? (Or having volatile registers). Well, it's *better* to provide defaults since otherwise everything defaults to 0 but it does avoid the whole allocation during fast path issue since it allocates the cache on init and perhaps that's OK. > So how to handle this properly? Bail out, if fast_io is available and > cache_type != (REGCACHE_NONE || REGCACHE_FLAT)? Or perhaps just if we have to do an allocation? I can see that someone might want to use an rbtree and would be careful enough to do the init, though I *am* a bit dubious about it. > > Why are you using a dynamically allocated rbtree for a device like this? > On my way home, I came to the same question. In fact this is not a > driver written by myself, but from here > http://git.freescale.com/git/cgit.cgi/ppc/sdk/linux.git/tree/drivers/video/fsl-dcu-fb.c#n1024. > I guess as this is a mmio device and things like regcache_cache_only() > are used, REGCACHE_FLAT seems appropriate. Ah, out of tree BSP code...
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