lkml.org 
[lkml]   [2022]   [Jan]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    SubjectRe: [PATCH v2 31/37] drm: rcar-du: Add support for the nomodeset kernel parameter
    From
    Hi

    Am 28.01.22 um 10:13 schrieb Kieran Bingham:
    > Hi Javier,
    >
    > Quoting Javier Martinez Canillas (2021-12-17 00:37:46)
    >> According to disable Documentation/admin-guide/kernel-parameters.txt, this
    >> parameter can be used to disable kernel modesetting.
    >>
    >> DRM drivers will not perform display-mode changes or accelerated rendering
    >> and only the system framebuffer will be available if it was set-up.
    >
    > What is the 'system framebuffer' in this instance? Reading
    > https://www.kernel.org/doc/Documentation/admin-guide/kernel-parameters.txt
    > it sounds like that means anything already set up by the bootloader.

    Exactly this.

    >
    >> But only a few DRM drivers currently check for nomodeset, make this driver
    >> to also support the command line parameter.
    >>
    >> Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
    >> ---
    >>
    >> (no changes since v1)
    >>
    >> drivers/gpu/drm/rcar-du/rcar_du_drv.c | 3 +++
    >> 1 file changed, 3 insertions(+)
    >>
    >> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_drv.c b/drivers/gpu/drm/rcar-du/rcar_du_drv.c
    >> index 5a8131ef81d5..982e450233ed 100644
    >> --- a/drivers/gpu/drm/rcar-du/rcar_du_drv.c
    >> +++ b/drivers/gpu/drm/rcar-du/rcar_du_drv.c
    >> @@ -701,6 +701,9 @@ static struct platform_driver rcar_du_platform_driver = {
    >>
    >> static int __init rcar_du_init(void)
    >> {
    >> + if (drm_firmware_drivers_only())
    >> + return -ENODEV;
    >> +
    >
    > This will completely disable all control of the display device when
    > nomodeset is enabled.
    >
    > Is there any requirement for us to support outputting to the display if
    > it was previously set up? presumably without setting or changing any
    > modes, but simply allowing the existing frame to be updated?

    There's no requirement for your driver. We just want a parameter where
    we can conveniently disable most of DRM's drivers and reduce it to a
    minimum. Helps distributions to provide a simple fallback mode. Most
    PCI-based drivers already support that. Now we're added it to the other
    drivers as well.

    >
    > I think the implication is that 'firmware drivers' would mean a display
    > could be updated through some firmware interface, which we won't have
    > ... so it seems reasonable to accept that this whole driver can be
    > disabled in that instance.

    It cannot be 'mode-setted'. We get a pre-configured framebuffer from the
    firmware or bootloader. Whatever we draw there shows up on the screen.

    Best regards
    Thomas


    >
    > Reading your mail that brought this thread up in my inbox, I think
    > you've already hit merge on this, so don't worry about adding a tag in
    > that instance, but I think this is ok.
    >
    > Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
    >
    >> rcar_du_of_init(rcar_du_of_table);
    >>
    >> return platform_driver_register(&rcar_du_platform_driver);
    >> --
    >> 2.33.1
    >>

    --
    Thomas Zimmermann
    Graphics Driver Developer
    SUSE Software Solutions Germany GmbH
    Maxfeldstr. 5, 90409 Nürnberg, Germany
    (HRB 36809, AG Nürnberg)
    Geschäftsführer: Ivo Totev
    [unhandled content-type:application/pgp-signature]
    \
     
     \ /
      Last update: 2022-01-28 10:35    [W:2.943 / U:0.268 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site