Le 31/08/2023 à 19:38, Christophe Leroy a écrit : > > > Le 31/08/2023 à 16:41, Thomas Zimmermann a écrit : >> Hi, >> >> there's a per-architecture function called fb_pgprotect() that sets >> VMA's vm_page_prot for mmaped framebuffers. Most architectures use a >> simple implementation based on pgprot_writecomine() [1] or >> pgprot_noncached(). [2] >> >> On PPC this function uses phys_mem_access_prot() and therefore >> requires the mmap call's file struct. [3] Removing the file argument >> would help with simplifying the caller of fb_pgprotect(). [4] >> >> Why is the file even required on PPC? >> >> Is it possible to replace phys_mem_access_prot() with something >> simpler that does not use the file struct? > > Looks like phys_mem_access_prot() defaults to calling pgprot_noncached() > see > https://elixir.bootlin.com/linux/v6.5/source/arch/powerpc/mm/mem.c#L37 > but for a few platforms that's superseeded by > pci_phys_mem_access_prot(), see > https://elixir.bootlin.com/linux/v6.5/source/arch/powerpc/kernel/pci-common.c#L524 > > However, as far as I can see pci_phys_mem_access_prot() doesn't use file > so you could likely drop that argument on phys_mem_access_prot() on > powerpc. But when I for instance look at arm, I see that the file > argument is used, see > https://elixir.bootlin.com/linux/v6.5/source/arch/arm/mm/mmu.c#L713 > > So, the simplest is maybe the following, allthough that's probably worth > a comment: > > diff --git a/arch/powerpc/include/asm/fb.h b/arch/powerpc/include/asm/fb.h > index 5f1a2e5f7654..8b9b856f476e 100644 > --- a/arch/powerpc/include/asm/fb.h > +++ b/arch/powerpc/include/asm/fb.h > @@ -6,10 +6,9 @@ > > #include <asm/page.h> > > -static inline void fb_pgprotect(struct file *file, struct > vm_area_struct *vma, > - unsigned long off) > +static inline void fb_pgprotect(struct vm_area_struct *vma, unsigned > long off) > { > - vma->vm_page_prot = phys_mem_access_prot(file, off >> PAGE_SHIFT, > + vma->vm_page_prot = phys_mem_access_prot(NULL, off >> PAGE_SHIFT, > vma->vm_end - vma->vm_start, > vma->vm_page_prot); > } And while at it, maybe also replace off >> PAGE_SHIFT by PHYS_PFN(off) Christophe > > > Christophe > > >> >> Best regards >> Thomas >> >> >> [1] >> https://elixir.bootlin.com/linux/v6.5/source/include/asm-generic/fb.h#L19 >> [2] >> https://elixir.bootlin.com/linux/v6.5/source/arch/mips/include/asm/fb.h#L11 >> [3] >> https://elixir.bootlin.com/linux/v6.5/source/arch/powerpc/include/asm/fb.h#L12 >> [4] >> https://elixir.bootlin.com/linux/v6.5/source/drivers/video/fbdev/core/fbmem.c#L1299 >> >>
