[PATCH v2] drm/ast: Fix soft lockup

[Jammy Huang]

Hi Thomas,

Thank you.

Regards,
Jammy Huang

> 
> Hi,
> 
> I've added a Fixes tag and pushed to patch into drm-misc-fixes.
> 
> Best regards
> Thomas
> 
> Am 03.04.24 um 11:02 schrieb Jammy Huang:
> > There is a while-loop in ast_dp_set_on_off() that could lead to
> > infinite-loop. This is because the register, VGACRI-Dx, checked in
> > this API is a scratch register actually controlled by a MCU, named
> > DPMCU, in BMC.
> >
> > These scratch registers are protected by scu-lock. If suc-lock is not
> > off, DPMCU can not update these registers and then host will have soft
> > lockup due to never updated status.
> >
> > DPMCU is used to control DP and relative registers to handshake with
> > host's VGA driver. Even the most time-consuming task, DP's link
> > training, is less than 100ms. 200ms should be enough.
> >
> > Signed-off-by: Jammy Huang <jammy_huang at aspeedtech.com>
> > Reviewed-by: Jocelyn Falempe <jfalempe at redhat.com>
> > ---
> >   drivers/gpu/drm/ast/ast_dp.c | 3 +++
> >   1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/ast/ast_dp.c
> > b/drivers/gpu/drm/ast/ast_dp.c index ebb6d8ebd44e..1e9259416980 100644
> > --- a/drivers/gpu/drm/ast/ast_dp.c
> > +++ b/drivers/gpu/drm/ast/ast_dp.c
> > @@ -180,6 +180,7 @@ void ast_dp_set_on_off(struct drm_device *dev, bool
> on)
> >   {
> >   	struct ast_device *ast = to_ast_device(dev);
> >   	u8 video_on_off = on;
> > +	u32 i = 0;
> >
> >   	// Video On/Off
> >   	ast_set_index_reg_mask(ast, AST_IO_VGACRI, 0xE3, (u8)
> > ~AST_DP_VIDEO_ENABLE, on); @@ -192,6 +193,8 @@ void
> ast_dp_set_on_off(struct drm_device *dev, bool on)
> >   						ASTDP_MIRROR_VIDEO_ENABLE) !=
> video_on_off) {
> >   			// wait 1 ms
> >   			mdelay(1);
> > +			if (++i > 200)
> > +				break;
> >   		}
> >   	}
> >   }
> >
> > base-commit: b0546776ad3f332e215cebc0b063ba4351971cca
> 
> --
> --
> 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)