Re: [PATCH] fbdev: efifb: do not load efifb if PCI BAR has changed but not fixuped

[Shixiong Ou <oushixiong1025@163.com>]

在 2025/7/7 17:28, Thomas Zimmermann 写道:
> Hi
>
> Am 07.07.25 um 11:24 schrieb Shixiong Ou:
>>
>> 在 2025/6/27 17:13, Thomas Zimmermann 写道:
>>> Hi
>>>
>>> Am 26.06.25 um 11:49 schrieb oushixiong1025@163.com:
>>>> From: Shixiong Ou <oushixiong@kylinos.cn>
>>>>
>>>> [WHY]
>>>> On an ARM machine, the following log is present:
>>>> [    0.900884] efifb: framebuffer at 0x1020000000, using 3072k, 
>>>> total 3072k
>>>> [    2.297884] amdgpu 0000:04:00.0: 
>>>> remove_conflicting_pci_framebuffers: bar 0: 0x1000000000 -> 
>>>> 0x100fffffff
>>>> [    2.297886] amdgpu 0000:04:00.0: 
>>>> remove_conflicting_pci_framebuffers: bar 2: 0x1010000000 -> 
>>>> 0x10101fffff
>>>> [    2.297888] amdgpu 0000:04:00.0: 
>>>> remove_conflicting_pci_framebuffers: bar 5: 0x58200000 -> 0x5823ffff
>>>>
>>>> It show that the efifb framebuffer base is out of PCI BAR, and this
>>>> results in both efi-framebuffer and amdgpudrmfb co-existing.
>>>>
>>>> The fbcon will be bound to efi-framebuffer by default and cannot be 
>>>> used.
>>>>
>>>> [HOW]
>>>> Do not load efifb driver if PCI BAR has changed but not fixuped.
>>>> In the following cases:
>>>>     1. screen_info_lfb_pdev is NULL.
>>>>     2. __screen_info_relocation_is_valid return false.
>>>
>>> Apart from ruling out invalid screen_info, did you figure out why 
>>> the relocation tracking didn't work? It would be good to fix this if 
>>> possible.
>>>
>>> Best regards
>>> Thomas
>>>
>> I haven’t figure out the root cause yet.
>>
>> This issue is quite rare and might be related to the EFI firmware.
>> However, I wonder if we could add some handling when no PCI resources 
>> are found in screen_info_fixup_lfb(), as a temporary workaround for 
>> the problem I mentioned earlier.
>
> As I said elsewhere in the thread, you can clear the screen_info's 
> video type in the branch at [1] to disable it entirely. We should have 
> probably done this anyway. Knowing the cause of the issue would still 
> be nice though.
>
> Best regards
> Thomas
>
> [1] 
> https://elixir.bootlin.com/linux/v6.15.5/source/drivers/video/screen_info_pci.c#L44 
>
>
thanks for you suggestion, while there are two cases:
     1. screen_info_lfb_pdev is NULL.
     2. __screen_info_relocation_is_valid return false.

should we do it at [1] too?

Best regards
Shixiong Ou

[1] 
https://elixir.bootlin.com/linux/v6.15.5/source/drivers/video/screen_info_pci.c#L47

>>
>> Best regards
>> Shixiong Ou
>>
>>>>
>>>> Signed-off-by: Shixiong Ou <oushixiong@kylinos.cn>
>>>> ---
>>>>   drivers/video/fbdev/efifb.c     |  4 ++++
>>>>   drivers/video/screen_info_pci.c | 24 ++++++++++++++++++++++++
>>>>   include/linux/screen_info.h     |  5 +++++
>>>>   3 files changed, 33 insertions(+)
>>>>
>>>> diff --git a/drivers/video/fbdev/efifb.c b/drivers/video/fbdev/efifb.c
>>>> index 0e1bd3dba255..de8d016c9a66 100644
>>>> --- a/drivers/video/fbdev/efifb.c
>>>> +++ b/drivers/video/fbdev/efifb.c
>>>> @@ -303,6 +303,10 @@ static void efifb_setup(struct screen_info 
>>>> *si, char *options)
>>>>     static inline bool fb_base_is_valid(struct screen_info *si)
>>>>   {
>>>> +    /* check whether fb_base has changed but not fixuped */
>>>> +    if (!screen_info_is_useful())
>>>> +        return false;
>>>> +
>>>>       if (si->lfb_base)
>>>>           return true;
>>>>   diff --git a/drivers/video/screen_info_pci.c 
>>>> b/drivers/video/screen_info_pci.c
>>>> index 66bfc1d0a6dc..ac57dcaf0cac 100644
>>>> --- a/drivers/video/screen_info_pci.c
>>>> +++ b/drivers/video/screen_info_pci.c
>>>> @@ -9,6 +9,8 @@ static struct pci_dev *screen_info_lfb_pdev;
>>>>   static size_t screen_info_lfb_bar;
>>>>   static resource_size_t screen_info_lfb_res_start; // original 
>>>> start of resource
>>>>   static resource_size_t screen_info_lfb_offset; // framebuffer 
>>>> offset within resource
>>>> +static bool screen_info_changed;
>>>> +static bool screen_info_fixuped;
>>>>     static bool __screen_info_relocation_is_valid(const struct 
>>>> screen_info *si, struct resource *pr)
>>>>   {
>>>> @@ -24,6 +26,24 @@ static bool 
>>>> __screen_info_relocation_is_valid(const struct screen_info *si, stru
>>>>       return true;
>>>>   }
>>>>   +bool screen_info_is_useful(void)
>>>> +{
>>>> +    unsigned int type;
>>>> +    const struct screen_info *si = &screen_info;
>>>> +
>>>> +    type = screen_info_video_type(si);
>>>> +    if (type != VIDEO_TYPE_EFI)
>>>> +        return true;
>>>> +
>>>> +    if (screen_info_changed && !screen_info_fixuped) {
>>>> +        pr_warn("The screen_info has changed but not fixuped");
>>>> +        return false;
>>>> +    }
>>>> +
>>>> +    pr_info("The screen_info is useful");
>>>> +    return true;
>>>> +}
>>>> +
>>>>   void screen_info_apply_fixups(void)
>>>>   {
>>>>       struct screen_info *si = &screen_info;
>>>> @@ -32,18 +52,22 @@ void screen_info_apply_fixups(void)
>>>>           struct resource *pr = 
>>>> &screen_info_lfb_pdev->resource[screen_info_lfb_bar];
>>>>             if (pr->start != screen_info_lfb_res_start) {
>>>> +            screen_info_changed = true;
>>>>               if (__screen_info_relocation_is_valid(si, pr)) {
>>>>                   /*
>>>>                    * Only update base if we have an actual
>>>>                    * relocation to a valid I/O range.
>>>>                    */
>>>>                   __screen_info_set_lfb_base(si, pr->start + 
>>>> screen_info_lfb_offset);
>>>> +                screen_info_fixuped = true;
>>>>                   pr_info("Relocating firmware framebuffer to 
>>>> offset %pa[d] within %pr\n",
>>>>                       &screen_info_lfb_offset, pr);
>>>>               } else {
>>>>                   pr_warn("Invalid relocating, disabling firmware 
>>>> framebuffer\n");
>>>>               }
>>>>           }
>>>> +    } else {
>>>> +        screen_info_changed = true;
>>>>       }
>>>>   }
>>>>   diff --git a/include/linux/screen_info.h 
>>>> b/include/linux/screen_info.h
>>>> index 923d68e07679..632cdbb1adbe 100644
>>>> --- a/include/linux/screen_info.h
>>>> +++ b/include/linux/screen_info.h
>>>> @@ -138,9 +138,14 @@ ssize_t screen_info_resources(const struct 
>>>> screen_info *si, struct resource *r,
>>>>   u32 __screen_info_lfb_bits_per_pixel(const struct screen_info *si);
>>>>     #if defined(CONFIG_PCI)
>>>> +bool screen_info_is_useful(void);
>>>>   void screen_info_apply_fixups(void);
>>>>   struct pci_dev *screen_info_pci_dev(const struct screen_info *si);
>>>>   #else
>>>> +bool screen_info_is_useful(void)
>>>> +{
>>>> +    return true;
>>>> +}
>>>>   static inline void screen_info_apply_fixups(void)
>>>>   { }
>>>>   static inline struct pci_dev *screen_info_pci_dev(const struct 
>>>> screen_info *si)
>>>
>>
>