On Tue, 14 Jul 2020 at 18:56, Thomas Zimmermann <tzimmermann@xxxxxxx> wrote: > > Hi > > Am 14.07.20 um 10:41 schrieb Daniel Vetter: > > On Tue, Jul 14, 2020 at 08:41:58AM +0200, Thomas Zimmermann wrote: > >> Hi > >> > >> Am 13.07.20 um 18:21 schrieb Daniel Vetter: > >>> On Fri, Jul 10, 2020 at 08:28:16AM +0200, Thomas Zimmermann wrote: > >>>> Hi > >>>> > >>>> Am 09.07.20 um 21:30 schrieb Sam Ravnborg: > >>>>> Mark reported that sparc64 would panic while booting using qemu. > >>>>> Mark bisected this to a patch that introduced generic fbdev emulation to > >>>>> the bochs DRM driver. > >>>>> Mark pointed out that a similar bug was fixed before where > >>>>> the sys helpers was replaced by cfb helpers. > >>>>> > >>>>> The culprint here is that the framebuffer reside in IO memory which > >>>>> requires SPARC ASI_PHYS (physical) loads and stores. > >>>>> > >>>>> The current bohcs DRM driver uses a shadow buffer. > >>>>> So all copying to the framebuffer happens in > >>>>> drm_fb_helper_dirty_blit_real(). > >>>>> > >>>>> The fix is to replace the memcpy with memcpy_toio() from io.h. > >>>>> > >>>>> memcpy_toio() uses writeb() where the original fbdev code > >>>>> used sbus_memcpy_toio(). The latter uses sbus_writeb(). > >>>>> > >>>>> The difference between writeb() and sbus_memcpy_toio() is > >>>>> that writeb() writes bytes in little-endian, where sbus_writeb() writes > >>>>> bytes in big-endian. As endian does not matter for byte writes they are > >>>>> the same. So we can safely use memcpy_toio() here. > >>>>> > >>>>> For many architectures memcpy_toio() is a simple memcpy(). > >>>>> One sideeffect that is unknow is if this has any impact on other > >>>>> architectures. > >>>>> So far the analysis tells that this change is OK for other arch's. > >>>>> but testing would be good. > >>>>> > >>>>> Signed-off-by: Sam Ravnborg <sam@xxxxxxxxxxxx> > >>>>> Reported-by: Mark Cave-Ayland <mark.cave-ayland@xxxxxxxxxxxx> > >>>>> Tested-by: Mark Cave-Ayland <mark.cave-ayland@xxxxxxxxxxxx> > >>>>> Cc: Mark Cave-Ayland <mark.cave-ayland@xxxxxxxxxxxx> > >>>>> Cc: Thomas Zimmermann <tzimmermann@xxxxxxx> > >>>>> Cc: Gerd Hoffmann <kraxel@xxxxxxxxxx> > >>>>> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx> > >>>>> Cc: sparclinux@xxxxxxxxxxxxxxx > >>>> > >>>> So this actually is a problem in practice. Do you know how userspace > >>>> handles this? > >>>> > >>>> For this patch > >>>> > >>>> Acked-by: Thomas Zimmermann <tzimmermann@xxxxxxx> > >>>> > >>>> but I'd like to have someone with more architecture expertise ack this > >>>> as well. > >>>> > >>>> Best regards > >>>> Thomas > >>>> > >>>>> --- > >>>>> drivers/gpu/drm/drm_fb_helper.c | 2 +- > >>>>> 1 file changed, 1 insertion(+), 1 deletion(-) > >>>>> > >>>>> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c > >>>>> index 5609e164805f..4d05b0ab1592 100644 > >>>>> --- a/drivers/gpu/drm/drm_fb_helper.c > >>>>> +++ b/drivers/gpu/drm/drm_fb_helper.c > >>>>> @@ -399,7 +399,7 @@ static void drm_fb_helper_dirty_blit_real(struct drm_fb_helper *fb_helper, > >>>>> unsigned int y; > >>>>> > >>>>> for (y = clip->y1; y < clip->y2; y++) { > >>>>> - memcpy(dst, src, len); > >>>>> + memcpy_toio(dst, src, len); > >>> > >>> I don't think we can do this unconditionally, there's fbdev-helper drivers > >>> using shmem helpers, and for shmem memcpy_toio is wrong. We need a switch > >>> to fix this properly I think. > >> > >> I once has a patch set for this problem, but it didn't make it. [1] > >> > >> Buffers can move between I/O and system memory, so a simple flag would > >> not work. I'd propose this > >> > >> bool drm_gem_is_iomem(struct drm_gem_object *obj) > >> { > >> if (obj->funcs && obj->funcs->is_iomem) > >> return obj->funcs->is_iomem(obj); > >> return false; > >> } > >> > >> Most GEM implmentations wouldn't bother, but VRAM helpers could set the > >> is_iomem function and return the current state. Fbdev helpers can then > >> pick the correct memcpy_*() function. > > > > Hm wasn't the (long term at least) idea to add the is_iomem flag to the > > vmap functions? is_iomem is kinda only well-defined if there's a vmap of > > the buffer around (which also pins it), or in general when the buffer is > > pinned. Outside of that an ->is_iomem function doesn't make much sense. > > Oh. From how I understood the original discussion, you shoot down the > idea because sparse would not support it well? > > The other idea was to add an additional vmap_iomem() helper that returns > an__iomem pointer. Can we try that? > Did we get anywhere with this yet? Dave. _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel