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

[Thomas Zimmermann <tzimmermann@suse.de>]

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

>
> 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)
>>
>

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)