Quoting Elliot Berman (2024-04-10 20:54:24) > On Thu, Mar 28, 2024 at 07:40:49PM -0500, Stephen Boyd wrote: > > Quoting Stephan Gerhold (2024-03-28 02:58:56) > > > > > > FWIW: This old patch series from Stephen Boyd is closely related: > > > https://lore.kernel.org/linux-arm-msm/20190910160903.65694-1-swboyd@xxxxxxxxxxxx/ > > > > > > > The main use case I have is to map the command-db memory region on > > > > Qualcomm devices with a read-only mapping. It's already a const marked > > > > pointer and the API returns const pointers as well, so this series > > > > makes sure that even stray writes can't modify the memory. > > > > > > Stephen, what was the end result of that patch series? Mapping the > > > cmd-db read-only sounds cleaner than trying to be lucky with the right > > > set of cache flags. > > > > > > > I dropped it because I got busy with other stuff. Feel free to pick it > > back up. It looks like the part where I left off was where we had to > > make the API fallback to mapping the memory as writeable if read-only > > isn't supported on the architecture. > [...] > > The other weird thing was that we passed both MEMREMAP_RO and > > MEMREMAP_WB to indicate what sort of fallback we want. Perhaps that can > > be encoded in the architecture layer so that you get the closest thing > > to read-only memory (i.e. any sort of write side caching is removed) and > > you don't have to pass a fallback mapping type. > > Was there any motivation for having the fallback? I suspect driver > owners that want to use MEMREMAP_RO will know which architectures the > driver is applicable to and also know whether MEMREMAP_RO would work. I don't think there was any motivation, but it has been many years so maybe I forgot. I suspect you're suggesting that we just don't do that and driver writers can call the memremap API another time if they want to implement a fallback? Sounds OK to me. > > > I also wanted to return a const pointer. > > The stash looks mostly complete. Do you think it should be part of the > series or submitted separately? > Make it part of the series so this topic can be finished? For example, it seems like iounmap() should have always taken a const pointer.
