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SubjectRe: [PATCH v10 06/12] peci: Add a PECI adapter driver for Aspeed AST24xx/AST25xx
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On 1/15/2019 3:14 PM, Joel Stanley wrote:
> On Tue, 15 Jan 2019 at 09:49, Jae Hyun Yoo <jae.hyun.yoo@linux.intel.com> 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

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