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
