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

[Tomi Valkeinen]

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.

 Tomi

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