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

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Date:   Tue, 22 Feb 2022 13:48:59 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Alex Elder <elder@...aro.org>
Cc:     mhi@...ts.linux.dev, quic_hemantk@...cinc.com,
        quic_bbhatt@...cinc.com, quic_jhugo@...cinc.com,
        vinod.koul@...aro.org, bjorn.andersson@...aro.org,
        dmitry.baryshkov@...aro.org, quic_vbadigan@...cinc.com,
        quic_cang@...cinc.com, quic_skananth@...cinc.com,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 15/25] bus: mhi: ep: Add support for processing MHI
 endpoint interrupts

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@...aro.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.

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.

> 					-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