Re: [PATCH] drm/ast: Fix ARM compatibility

[Jammy Huang]

Hi Thomas,

Thanks for you reminder. The comment you mentioned is added in 2014 for 
AST2400 rev 0x20, which means MMIO is not enable by default before that 
revision. I will send another patch to handle it.


On 2023/4/18 下午 03:24, Thomas Zimmermann wrote:
> Hi
>
> Am 18.04.23 um 03:23 schrieb Jammy Huang:
> > Hi Thomas,
> >
> > The Intel(x86) CPUs have a separate address space for "IO", but the 
> > ARM architecture only has "memory", so all IO devices are accessed as 
> > if they were memory. Which means ARM does not support isolated IO. 
> > Here is a related discussion on ARM's forum.
> >
> > https://community.arm.com/support-forums/f/architectures-and-processors-forum/52046/how-to-read-write-an-i-o-port-in-aarch64 
> >
> >
> > Thus, we want to adapt MMIO only after this patch.
>
> What I mean is that there's a comment that says "assume the chip has 
> MMIO enabled by default (rev 0x20 and higher)". We also support revs 
> before 0x20. What happens to them?
>
> Best regards
> Thomas
>
> > On 2023/4/17 下午 07:51, Thomas Zimmermann wrote:
> > > Hi
> > >
> > > Am 07.04.23 um 04:09 schrieb Jammy Huang:
> > > > Hi Thomas,
> > > >
> > > > Could you help review this patch??
> > > >
> > > > We met some problem on nvidia's ARM platfrom and need this patch to 
> > > > fix it.
> > > >
> > > > On 2023/3/2 上午 10:19, Jammy Huang wrote:
> > > > > ARM architecture only has 'memory', so all devices are accessed by 
> > > > > MMIO.
> > > > >
> > > > > Signed-off-by: Jammy Huang <jammy_huang@xxxxxxxxxxxxxx>
> > > > > ---
> > > > >   drivers/gpu/drm/ast/ast_main.c | 17 +----------------
> > > > >   1 file changed, 1 insertion(+), 16 deletions(-)
> > > > >
> > > > > diff --git a/drivers/gpu/drm/ast/ast_main.c 
> > > > > b/drivers/gpu/drm/ast/ast_main.c
> > > > > index 794ffd4a29c5..f86d01e9f024 100644
> > > > > --- a/drivers/gpu/drm/ast/ast_main.c
> > > > > +++ b/drivers/gpu/drm/ast/ast_main.c
> > > > > @@ -424,22 +424,7 @@ struct ast_device *ast_device_create(const 
> > > > > struct drm_driver *drv,
> > > > >       if (!ast->regs)
> > > > >           return ERR_PTR(-EIO);
> > > > > -    /*
> > > > > -     * If we don't have IO space at all, use MMIO now and
> > > > > -     * assume the chip has MMIO enabled by default (rev 0x20
> > > > > -     * and higher).
> > > > > -     */
> > > > > -    if (!(pci_resource_flags(pdev, 2) & IORESOURCE_IO)) {
> > > > > -        drm_info(dev, "platform has no IO space, trying MMIO\n");
> > > > > -        ast->ioregs = ast->regs + AST_IO_MM_OFFSET;
> > > > > -    }
> > > > > -
> > > > > -    /* "map" IO regs if the above hasn't done so already */
> > > > > -    if (!ast->ioregs) {
> > > > > -        ast->ioregs = pcim_iomap(pdev, 2, 0);
> > >
> > > What happens on systems that use this branch?
> > >
> > > Best regards
> > > Thomas
> > >
> > > > > -        if (!ast->ioregs)
> > > > > -            return ERR_PTR(-EIO);
> > > > > -    }
> > > > > +    ast->ioregs = ast->regs + AST_IO_MM_OFFSET;
> > > > >       ast_detect_chip(dev, &need_post);
> > > > >
> > > > > base-commit: 254986e324add8a30d0019c6da59f81adc8b565f
> > --
> > Best Regards
> > Jammy
--
Best Regards
Jammy