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

[Shixiong Ou <oushixiong1025@163.com>]

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.

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)
>