[PATCH] fbdev: efifb: do not load efifb if PCI BAR has changed but not fixuped
Thomas Zimmermann
tzimmermann at suse.de
Mon Jul 7 10:17:14 UTC 2025
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 at 163.com:
>>>>> From: Shixiong Ou <oushixiong at 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 at 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)
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