Re: [PATCH v3 15/25] bus: mhi: ep: Add support for processing MHI endpoint interrupts

Alex Elder
2022-02-22T14:09:11Z

On 2/22/22 2:18 AM, Manivannan Sadhasivam wrote:
> On Tue, Feb 15, 2022 at 04:39:30PM -0600, Alex Elder wrote:
>> On 2/12/22 12:21 PM, Manivannan Sadhasivam wrote:
>>> Add support for processing MHI endpoint interrupts such as control
>>> interrupt, command interrupt and channel interrupt from the host.
>>>
>>> The interrupts will be generated in the endpoint device whenever host
>>> writes to the corresponding doorbell registers. The doorbell logic
>>> is handled inside the hardware internally.
>>>
>>> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
>>
>> Unless I'm mistaken, you have some bugs here.
>>
>> Beyond that, I question whether you should be using workqueues
>> for handling all interrupts. For now, it's fine, but there
>> might be room for improvement after this is accepted upstream
>> (using threaded interrupt handlers, for example).
>>
>
> Only reason I didn't use bottom halves is that the memory for TRE buffers need
> to be allocated each time, so essentially the caller should not sleep.

Threaded interrupt handlers can sleep. If scheduled, they run
immediately after hard interrupt handlers. For receive buffers,
yes, replacing a receive buffer just consumed would require an
allocation, but for transmit I think it might be possible to
avoid the need to do a memory allocation. (Things to think
about at some future date.)

> This is currently a limitation of iATU where there are only 8 windows for
> mapping the host memory and each memory region size is also limited.

Those are hard limitations, and probably what constrains you the most.

-Alex
>
>> -Alex
>>
>>> ---
>>> drivers/bus/mhi/ep/main.c | 113 +++++++++++++++++++++++++++++++++++++-
>>> include/linux/mhi_ep.h | 2 +
>>> 2 files changed, 113 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/bus/mhi/ep/main.c b/drivers/bus/mhi/ep/main.c
>>> index ccb3c2795041..072b872e735b 100644
>>> --- a/drivers/bus/mhi/ep/main.c
>>> +++ b/drivers/bus/mhi/ep/main.c
>>> @@ -185,6 +185,56 @@ static void mhi_ep_ring_worker(struct work_struct *work)
>>> }
>>> }
>>> +static void mhi_ep_queue_channel_db(struct mhi_ep_cntrl *mhi_cntrl,
>>> + unsigned long ch_int, u32 ch_idx)
>>> +{
>>> + struct device *dev = &mhi_cntrl->mhi_dev->dev;
>>> + struct mhi_ep_ring_item *item;
>>> + struct mhi_ep_ring *ring;
>>> + unsigned int i;
>>
>> Why not u32 i? And why is the ch_int argument unsigned long? The value
>> passed in is a u32.
>>
>
> for_each_set_bit() expects the 2nd argument to be of type "unsigned long".
>
> Thanks,
> Mani