Re: [PATCH] bus: mhi: Command completion workaround

[Jeffrey Hugo <jhugo@codeaurora.org>]

On 3/11/2021 1:05 AM, Loic Poulain wrote:
> Hi Jeffrey,
> 
> On Wed, 10 Mar 2021 at 17:19, Jeffrey Hugo <jhugo@codeaurora.org> wrote:
>>
>> On 3/10/2021 4:38 AM, Loic Poulain wrote:
>>> Some buggy hardwares (e.g sdx24) may report the current command
>>> ring wp pointer instead of the command completion pointer. It's
>>> obviously wrong, causing completion timeout. We can however deal
>>> with that situation by completing the cmd n-1 element, which is
>>> what the device actually completes.
>>>
>>> Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
>>> ---
>>>    drivers/bus/mhi/core/main.c | 18 ++++++++++++++++++
>>>    1 file changed, 18 insertions(+)
>>>
>>> diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
>>> index 16b9640..3e3c520 100644
>>> --- a/drivers/bus/mhi/core/main.c
>>> +++ b/drivers/bus/mhi/core/main.c
>>> @@ -707,6 +707,7 @@ static void mhi_process_cmd_completion(struct mhi_controller *mhi_cntrl,
>>>    {
>>>        dma_addr_t ptr = MHI_TRE_GET_EV_PTR(tre);
>>>        struct mhi_cmd *cmd_ring = &mhi_cntrl->mhi_cmd[PRIMARY_CMD_RING];
>>> +     struct device *dev = &mhi_cntrl->mhi_dev->dev;
>>>        struct mhi_ring *mhi_ring = &cmd_ring->ring;
>>>        struct mhi_tre *cmd_pkt;
>>>        struct mhi_chan *mhi_chan;
>>> @@ -714,6 +715,23 @@ static void mhi_process_cmd_completion(struct mhi_controller *mhi_cntrl,
>>>
>>>        cmd_pkt = mhi_to_virtual(mhi_ring, ptr);
>>>
>>> +     if (unlikely(cmd_pkt == mhi_ring->wp)) {
>>> +             /* Some buggy hardwares (e.g sdx24) sometimes report the current
>>> +              * command ring wp pointer instead of the command completion
>>> +              * pointer. It's obviously wrong, causing completion timeout. We
>>> +              * can however deal with that situation by completing the cmd
>>> +              * n-1 element.
>>> +              */
>>> +             void *ring_ptr = (void *)cmd_pkt - mhi_ring->el_size;
>>> +
>>> +             if (ring_ptr < mhi_ring->base)
>>> +                     ring_ptr += mhi_ring->len;
>>> +
>>> +             cmd_pkt = ring_ptr;
>>> +
>>> +             dev_warn(dev, "Bad completion pointer (ptr == ring_wp)\n");
>>
>> Is there value in having this warning every time?  I wonder if a _once
>> version would be better to not flood the kernel log.  Although this is
>> only for commands, which shouldn't be frequent, so maybe that is the
>> implicit rate limiter.
>>
>> What do you think?
> 
> As you said it's kind of self rate-limited because of the unfrequent
> command operations, mostly for starting and stopping channels. A _once
> variant would hide the issue a bit, and probably not annoying enough
> to raise curiosity.

Thats fair.

I happened to notice just now that the block comment you have above is 
not the proper style.  That looks like the netdev style, but we are not 
in the netdev area.

I'm curious to see where you and Hemant land on his comment.

-- 
Jeffrey Hugo
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.