Re: [PATCH v2 2/2] usb: dwc2: host: Clear interrupts before handling them

Doug Anderson
2015-11-19T16:37:36Z

Hi,

On Wed, Nov 18, 2015 at 5:43 PM, John Youn <John.Youn@synopsys.com> wrote:
> On 11/16/2015 9:22 AM, Doug Anderson wrote:
>> Felipe,
>>
>> On Mon, Nov 16, 2015 at 8:28 AM, Felipe Balbi <balbi@ti.com> wrote:
>>>
>>> Hi,
>>>
>>> Douglas Anderson <dianders@chromium.org> writes:
>>>> In general it is wise to clear interrupts before processing them. If
>>>> you don't do that, you can get:
>>>> 1. Interrupt happens
>>>> 2. You look at system state and process interrupt
>>>> 3. A new interrupt happens
>>>> 4. You clear interrupt without processing it.
>>>>
>>>> This patch was actually a first attempt to fix missing device insertions
>>>> as described in (usb: dwc2: host: Fix missing device insertions) and it
>>>> did solve some of the signal bouncing problems but not all of
>>>> them (which is why I submitted the other patch). Specifically, this
>>>> patch itself would sometimes change:
>>>> 1. hardware sees connect
>>>> 2. hardware sees disconnect
>>>> 3. hardware sees connect
>>>> 4. dwc2_port_intr() - clears connect interrupt
>>>> 5. dwc2_handle_common_intr() - calls dwc2_hcd_disconnect()
>>>>
>>>> ...to:
>>>> 1. hardware sees connect
>>>> 2. hardware sees disconnect
>>>> 3. dwc2_port_intr() - clears connect interrupt
>>>> 4. hardware sees connect
>>>> 5. dwc2_handle_common_intr() - calls dwc2_hcd_disconnect()
>>>>
>>>> ...but with different timing then sometimes we'd still miss cable
>>>> insertions.
>>>>
>>>> In any case, though this patch doesn't fix any (known) problems, it
>>>> still seems wise as a general policy to clear interrupt before handling
>>>> them.
>>>>
>>>> Signed-off-by: Douglas Anderson <dianders@chromium.org>
>>>> ---
>>>> Changes in v2: None
>>>>
>>>> drivers/usb/dwc2/core_intr.c | 55 ++++++++++++++++++++++----------------------
>>>> drivers/usb/dwc2/hcd_intr.c | 16 ++++++-------
>>>> 2 files changed, 35 insertions(+), 36 deletions(-)
>>>>
>>>> diff --git a/drivers/usb/dwc2/core_intr.c b/drivers/usb/dwc2/core_intr.c
>>>> index 61601d16e233..2a166b7eec41 100644
>>>> --- a/drivers/usb/dwc2/core_intr.c
>>>> +++ b/drivers/usb/dwc2/core_intr.c
>>>> @@ -80,15 +80,16 @@ static const char *dwc2_op_state_str(struct dwc2_hsotg *hsotg)
>>>> */
>>>> static void dwc2_handle_usb_port_intr(struct dwc2_hsotg *hsotg)
>>>> {
>>>> - u32 hprt0 = dwc2_readl(hsotg->regs + HPRT0);
>>>> + u32 hprt0;
>>>>
>>>> + /* Clear interrupt */
>>>> + dwc2_writel(GINTSTS_PRTINT, hsotg->regs + GINTSTS);
>>>> +
>>>> + hprt0 = dwc2_readl(hsotg->regs + HPRT0);
>>>> if (hprt0 & HPRT0_ENACHG) {
>>>> hprt0 &= ~HPRT0_ENA;
>>>> dwc2_writel(hprt0, hsotg->regs + HPRT0);
>>>> }
>>>> -
>>>> - /* Clear interrupt */
>>>> - dwc2_writel(GINTSTS_PRTINT, hsotg->regs + GINTSTS);
>>>
>>> isn't this a regression ? You're first clearing the interrupts and only
>>> then reading to check what's pending, however, what's pending has just
>>> been cleared. Seems like this should be:
>>>
>>> hprt0 = dwc2_readl(HPRT0);
>>> dwc2_writeal(PRTINT, GINTSTS);
>>
>> Actually, we could probably remove the setting of GINTSTS_PRTINT
>> completely. The docs I have say that the GINTSTS_PRTINT is read only
>> and that:
>>
>>> The core sets this bit to indicate a change in port status of one of the
>>> DWC_otg core ports in Host mode. The application must read the
>>> Host Port Control and Status (HPRT) register to determine the exact
>>> event that caused this interrupt. The application must clear the
>>> appropriate status bit in the Host Port Control and Status register to
>>> clear this bit.
>>
>> ...so writing PRTINT is probably useless, but John can confirm.
>>
>
> Yup, it seems it can be removed.

How do you guys want this handled? Should I send up a new version of
this patch? ...or should I send a followon patch that does this
removal?

-Doug