[PATCH v2 6/6] drm/bridge: cdns-mhdp8546: Fix the interrupt enable/disable

[Nikhil Devshatwar]

On 14:27-20201110, Tomi Valkeinen wrote:
> On 10/11/2020 12:27, Nikhil Devshatwar wrote:
> > On 11:21-20201110, Tomi Valkeinen wrote:
> >> On 09/11/2020 19:06, Nikhil Devshatwar wrote:
> >>> When removing the tidss driver, there is a warning reported by
> >>> kernel about an unhandled interrupt for mhdp driver.
> >>>
> >>> [   43.238895] irq 31: nobody cared (try booting with the "irqpoll" option)
> >>> ... [snipped backtrace]
> >>> [   43.330735] handlers:
> >>> [   43.333020] [<000000005367c4f9>] irq_default_primary_handler threaded [<000000007e02b601>]
> >>> cdns_mhdp_irq_handler [cdns_mhdp8546]
> >>> [   43.344607] Disabling IRQ #31
> >>>
> >>> This happens because as part of cdns_mhdp_bridge_hpd_disable, driver tries
> >>> to disable the interrupts. While disabling the SW_EVENT interrupts,
> >>> it accidentally enables the MBOX interrupts, which are not handled by
> >>> the driver.
> >>>
> >>> Fix this with a read-modify-write to update only required bits.
> >>> Do the same for enabling interrupts as well.
> >>>
> >>> Signed-off-by: Nikhil Devshatwar <nikhil.nd at ti.com>
> >>> ---
> >>>  drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c | 7 +++++--
> >>>  1 file changed, 5 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c b/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
> >>> index 2cd809eed827..6beccd2a408e 100644
> >>> --- a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
> >>> +++ b/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
> >>> @@ -2146,7 +2146,8 @@ static void cdns_mhdp_bridge_hpd_enable(struct drm_bridge *bridge)
> >>>  
> >>>  	/* Enable SW event interrupts */
> >>>  	if (mhdp->bridge_attached)
> >>> -		writel(~(u32)CDNS_APB_INT_MASK_SW_EVENT_INT,
> >>> +		writel(readl(mhdp->regs + CDNS_APB_INT_MASK) &
> >>> +		       ~CDNS_APB_INT_MASK_SW_EVENT_INT,
> >>>  		       mhdp->regs + CDNS_APB_INT_MASK);
> >>>  }
> >>>  
> >>> @@ -2154,7 +2155,9 @@ static void cdns_mhdp_bridge_hpd_disable(struct drm_bridge *bridge)
> >>>  {
> >>>  	struct cdns_mhdp_device *mhdp = bridge_to_mhdp(bridge);
> >>>  
> >>> -	writel(CDNS_APB_INT_MASK_SW_EVENT_INT, mhdp->regs + CDNS_APB_INT_MASK);
> >>> +	writel(readl(mhdp->regs + CDNS_APB_INT_MASK) |
> >>> +	       CDNS_APB_INT_MASK_SW_EVENT_INT,
> >>> +	       mhdp->regs + CDNS_APB_INT_MASK);
> >>>  }
> >>>  
> >>>  static const struct drm_bridge_funcs cdns_mhdp_bridge_funcs = {
> >>
> >> Good catch. I wonder why we need the above functions... We already enable and disable the interrupts
> >> when attaching/detaching the driver. And I think we want to get the interrupt even if we won't
> >> report HPD (but I think we always do report it), as we need the interrupts to track the link status.
> >>
> > 
> > I read from the code that there is TODO for handling the mailbox
> > interrupts in the driver. Once that is supported, you will be able to
> > explictily enable/disable interrupts for SW_EVENTS (like hotplug) as
> > well as mailbox events. This enabling specific bits in the interrupt
> > status.
> 
> But SW_EVENTS is not the same as HPD, at least in theory. If we disable SW_EVENT_INT in
> hpd_disable(), we lose all SW_EVENT interrupts.

I am not sure, what exactly is covered in the SW events apart from the hotplug.

Swapnil, Yuti, Please fill in..

Nikhil D
> 
>  Tomi
> 
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