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    Subject[PATCH 5.15 223/279] fbdev: Prevent probing generic drivers if a FB is already registered
    Date
    From: Javier Martinez Canillas <javierm@redhat.com>

    commit fb561bf9abde49f7e00fdbf9ed2ccf2d86cac8ee upstream.

    The efifb and simplefb drivers just render to a pre-allocated frame buffer
    and rely on the display hardware being initialized before the kernel boots.

    But if another driver already probed correctly and registered a fbdev, the
    generic drivers shouldn't be probed since an actual driver for the display
    hardware is already present.

    This is more likely to occur after commit d391c5827107 ("drivers/firmware:
    move x86 Generic System Framebuffers support") since the "efi-framebuffer"
    and "simple-framebuffer" platform devices are registered at a later time.

    Link: https://lore.kernel.org/r/20211110200253.rfudkt3edbd3nsyj@lahvuun/
    Fixes: d391c5827107 ("drivers/firmware: move x86 Generic System Framebuffers support")
    Reported-by: Ilya Trukhanov <lahvuun@gmail.com>
    Cc: <stable@vger.kernel.org> # 5.15.x
    Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
    Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
    Tested-by: Ilya Trukhanov <lahvuun@gmail.com>
    Link: https://patchwork.freedesktop.org/patch/msgid/20211111115757.1351045-1-javierm@redhat.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/video/fbdev/efifb.c | 11 +++++++++++
    drivers/video/fbdev/simplefb.c | 11 +++++++++++
    2 files changed, 22 insertions(+)

    --- a/drivers/video/fbdev/efifb.c
    +++ b/drivers/video/fbdev/efifb.c
    @@ -351,6 +351,17 @@ static int efifb_probe(struct platform_d
    char *option = NULL;
    efi_memory_desc_t md;

    + /*
    + * Generic drivers must not be registered if a framebuffer exists.
    + * If a native driver was probed, the display hardware was already
    + * taken and attempting to use the system framebuffer is dangerous.
    + */
    + if (num_registered_fb > 0) {
    + dev_err(&dev->dev,
    + "efifb: a framebuffer is already registered\n");
    + return -EINVAL;
    + }
    +
    if (screen_info.orig_video_isVGA != VIDEO_TYPE_EFI || pci_dev_disabled)
    return -ENODEV;

    --- a/drivers/video/fbdev/simplefb.c
    +++ b/drivers/video/fbdev/simplefb.c
    @@ -407,6 +407,17 @@ static int simplefb_probe(struct platfor
    struct simplefb_par *par;
    struct resource *mem;

    + /*
    + * Generic drivers must not be registered if a framebuffer exists.
    + * If a native driver was probed, the display hardware was already
    + * taken and attempting to use the system framebuffer is dangerous.
    + */
    + if (num_registered_fb > 0) {
    + dev_err(&pdev->dev,
    + "simplefb: a framebuffer is already registered\n");
    + return -EINVAL;
    + }
    +
    if (fb_get_options("simplefb", NULL))
    return -ENODEV;


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