Re: [PATCH v4 2/2] usb: dwc2: host: Clear interrupts before handling them

From: Doug Anderson
Date: Fri Nov 20 2015 - 11:49:22 EST


On Fri, Nov 20, 2015 at 7:40 AM, Felipe Balbi <balbi@xxxxxx> wrote:
> Hi,
> Douglas Anderson <dianders@xxxxxxxxxxxx> 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()
>> 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.
>> Note that for dwc2_handle_usb_port_intr(), instead of moving the clear
>> of PRTINT to the beginning of the function we remove it completely. The
>> only way to clear PRTINT is to clear the sources that set it in the
>> first place.
>> Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
>> Acked-by: John Youn <johnyoun@xxxxxxxxxxxx>
>> Tested-by: John Youn <johnyoun@xxxxxxxxxxxx>
> $ patch -p1 --dry-run < patch.diff
> checking file drivers/usb/dwc2/core_intr.c
> checking file drivers/usb/dwc2/hcd_intr.c
> Hunk #4 FAILED at 365.
> Hunk #5 succeeded at 388 (offset 11 lines).
> 1 out of 5 hunks FAILED
> Care to rebase on top of my testing/next ?

No problem.

...though when I did that, I actually found (by code inspection) a bug
in the original patch, so I guess it's a good thing it didn't apply...
...and then that led me to another bug that was pre-existing. I'll
send up two new patches shortly. I'll remove John's Ack and Tested
tags from the patch since it contains a change.

It looks like you already landed part 1 of this series (usb: dwc2:
host: Fix missing device insertions) so I won't resend that.

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