Re: [PATCH v10 06/12] peci: Add a PECI adapter driver for Aspeed AST24xx/AST25xx

[Jae Hyun Yoo]

On 1/15/2019 3:14 PM, Joel Stanley wrote:
> On Tue, 15 Jan 2019 at 09:49, Jae Hyun Yoo <jae.hyun.yoo@xxxxxxxxxxxxxxx> wrote:
> > > > +       /**
> > > > +        * We check that the regmap works on this very first access,
> > > > +        * but as this is an MMIO-backed regmap, subsequent regmap
> > > > +        * access is not going to fail and we skip error checks from
> > > > +        * this point.
> > >
> > > Why do you use a regmap for this driver? AFAICT it has exclusive
> > > ownership over the register range it uses, which is sometimes a reason
> > > to use a regmap over a mmio region.
> > >
> > > I'm not sure if you've ever disassembled drivers/base/regmap/regmap.o,
> > > but if you do you will find that a single mmio read turns into
> > > hundreds of instructions.
> >
> > No specific reason. regmap makes some overhead as you mentioned but it
> > also provides some advantages on access simplification, endianness
> > handling and register dump at run time. I would not insist using of
> > regmap if you prefer using of raw readl and writel. Do you want replace
> > regmap with readl and writel in this driver?
>
> I think that would be best.
>
> You raise some good points about the regmap API, and you're not alone
> in using it for these reasons. We should look in to providing a
> suitable API without the overhead, or making regmap more efficient for
> the mmio case.

Okay. I'll rewrite this driver code using readl and writel instead of 
regmap mmio. Thanks again for your review!

Regards,
Jae