On Thu, Mar 08, 2018 at 03:16:29AM +0000, French, Nicholas A. wrote: > On Wed, Mar 07, 2018 at 07:02:05PM +0000, Luis R. Rodriguez wrote: > > On Tue, Mar 06, 2018 at 09:01:10PM +0000, French, Nicholas A. wrote: > > > any reason why PAT can't be enabled for ivtvfb as simply as in the attached > > > patch? > > > > Prior to your change the OSD buffer was obtained using the itv->dec_mem + oi->video_rbase > > given itv->dec_mem was initialized via [...] > > itv->dec_mem = ioremap_nocache(itv->base_addr + IVTV_DECODER_OFFSET - oi->video_buffer_size, > > IVTV_DECODER_SIZE); > > Ah, I see. So my proposed ioremap_wc call was only "working" by aliasing the > ioremap_nocache()'d mem area and not actually using write combining at all. There are some debugging PAT toys out there I think but I haven't played with them yet or I forgot how to to confirm or deny this sort of effort, but likeley. > > So what I'd do is change the ioremap_nocache()'d size by substracting > > oi->video_buffer_size -- but then you have to ask yourself how you'd get > > that size. If its something you can figure out then great. > > Size is easy since its hardcoded, but unfortunately getting the offset of the > framebuffer inside the decoders memory to remove from the ioremap_nocache > call is a chicken and egg problem: the offset is determined by querying the > firmware that has been loaded to the decoder. the firmware itself will be > loaded after the ioremap_nocache call at an offset from the address it > returns. What I expected. Probably why no one had tried before to clean it up. > So unless there is a io-re-remap to change the caching status of a subset of > the decoder's memory once we find out what the framebuffer offset is inside > the original iremap_nocache'd area, then its a no go for write combining to > the framebuffer with PAT. No what if the framebuffer driver is just requested as a secondary step after firmware loading? > On the other hand, it works fine for me with a nocache'd framebuffer. It's > certainly better for me personally to have a nocache framebuffer with > PAT-enabled than the framebuffer completely disabled with PAT-enabled, but I > don't think I would even propose to rollback the x86 nopat requirement in > general. Apparently the throngs of people using this super-popular driver > feature haven't complained in the last couple years, so maybe its OK for me > to just patch the pat-enabled guard out and deal with a nocache'd > framebuffer. Nope, best you add a feature to just let you disable wc stuff, to enable life with PAT. Luis
