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

[Jammy Huang <jammy_huang@aspeedtech.com>]

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@aspeedtech.com>
>>>>> ---
>>>>>   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