[PATCH] drm: mxsfb: Clear FIFO_CLEAR bit

[Lucas Stach]

Am Montag, dem 21.06.2021 um 18:30 +0200 schrieb Marek Vasut:
> On 6/21/21 2:14 PM, Lucas Stach wrote:
> 
> [...]
> 
> > > diff --git a/drivers/gpu/drm/mxsfb/mxsfb_kms.c b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> > > index 98d8ba0bae84..22cb749fc9bc 100644
> > > --- a/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> > > +++ b/drivers/gpu/drm/mxsfb/mxsfb_kms.c
> > > @@ -241,6 +241,9 @@ static void mxsfb_crtc_mode_set_nofb(struct mxsfb_drm_private *mxsfb,
> > >   
> > >   	/* Clear the FIFOs */
> > >   	writel(CTRL1_FIFO_CLEAR, mxsfb->base + LCDC_CTRL1 + REG_SET);
> > > +	readl(mxsfb->base + LCDC_CTRL1);
> > 
> > Do you really need those readbacks? As both writes are targeting the
> > same slave interface, the memory barrier in the clear write should push
> > the set write.
> 
> What would push the clear write then ? We can drop one of the readl()s, 
> but not the last one.

There are a lot of more writes with barriers to the controller slave
interface in that function after clearing the FIFO. I don't see why
this readback would be required.

Regards,
Lucas