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 12:02 schrieb Shixiong Ou:
>
> 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?

No. This being NULL is an entirely valid state.

Best regards
Thomas

>
> 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)
>>>>
>>>
>>
>
>

-- 
--
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)