Re: [PATCH v3 1/3] bus: mhi: core: Introduce internal register poll helper function

[Bhaumik Bhatt <bbhatt@xxxxxxxxxxxxxx>]

On 2021-03-10 10:57 AM, Jeffrey Hugo wrote:
> On 2/23/2021 8:44 PM, Bhaumik Bhatt wrote:
> > Introduce helper function to allow MHI core driver to poll for
> > a value in a register field. This helps reach a common path to
> > read and poll register values along with a retry time interval.
> >
> > Signed-off-by: Bhaumik Bhatt <bbhatt@xxxxxxxxxxxxxx>
> > ---
> >   drivers/bus/mhi/core/internal.h |  3 +++
> >   drivers/bus/mhi/core/main.c     | 23 +++++++++++++++++++++++
> >   2 files changed, 26 insertions(+)
> >
> > diff --git a/drivers/bus/mhi/core/internal.h 
> > b/drivers/bus/mhi/core/internal.h
> > index 6f80ec3..005286b 100644
> > --- a/drivers/bus/mhi/core/internal.h
> > +++ b/drivers/bus/mhi/core/internal.h
> > @@ -643,6 +643,9 @@ int __must_check mhi_read_reg(struct 
> > mhi_controller *mhi_cntrl,
> >   int __must_check mhi_read_reg_field(struct mhi_controller 
> > *mhi_cntrl,
> >   				    void __iomem *base, u32 offset, u32 mask,
> >   				    u32 shift, u32 *out);
> > +int __must_check mhi_poll_reg_field(struct mhi_controller *mhi_cntrl,
> > +				    void __iomem *base, u32 offset, u32 mask,
> > +				    u32 shift, u32 val, u32 delayus);
> >   void mhi_write_reg(struct mhi_controller *mhi_cntrl, void __iomem 
> > *base,
> >   		   u32 offset, u32 val);
> >   void mhi_write_reg_field(struct mhi_controller *mhi_cntrl, void 
> > __iomem *base,
> > diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
> > index 4e0131b..249ae26 100644
> > --- a/drivers/bus/mhi/core/main.c
> > +++ b/drivers/bus/mhi/core/main.c
> > @@ -4,6 +4,7 @@
> >    *
> >    */
> >   +#include <linux/delay.h>
> >   #include <linux/device.h>
> >   #include <linux/dma-direction.h>
> >   #include <linux/dma-mapping.h>
> > @@ -37,6 +38,28 @@ int __must_check mhi_read_reg_field(struct 
> > mhi_controller *mhi_cntrl,
> >   	return 0;
> >   }
> >   +int __must_check mhi_poll_reg_field(struct mhi_controller 
> > *mhi_cntrl,
> > +				    void __iomem *base, u32 offset,
> > +				    u32 mask, u32 shift, u32 val, u32 delayus)
> > +{
> > +	int ret = -ENOENT;
Make this int ret;
> > +	u32 out, retry = (mhi_cntrl->timeout_ms * 1000) / delayus;
> > +
> > +	while (retry--) {
> > +		ret = mhi_read_reg_field(mhi_cntrl, base, offset, mask, shift,
> > +					 &out);
> > +		if (ret)
> > +			return -EIO;
>
> I generally dislike recoding return codes.  Do you believe it adds
> value here?  I'm concerned that if I'm debugging an error, I'll get
> EIO, which I trace to here, but then I don't know what the actual
> error from mhi_read_reg_field() was.
Thanks for pointing out. I don't think its necessary to recode and I can 
go back
to returning whatever the reg_field API returns. I have added the 
proposed changes
here which help fix a potential bug that we'd return 0 if read is 
successful but
polling fails.
> > +
> > +		if (out == val)
> > +			return 0;
> > +
> > +		udelay(delayus);
> > +	}
> > +
> > +	return ret;
return -ENOENT; to signify failure to find the entry after poll duration 
completes
> > +}
> > +
> >   void mhi_write_reg(struct mhi_controller *mhi_cntrl, void __iomem 
> > *base,
> >   		   u32 offset, u32 val)
> >   {

Thanks,
Bhaumik
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