Re: [PATCH v11 2/9] mmc: cavium: Add core MMC driver for Cavium SOCs

From: Ulf Hansson
Date: Wed Mar 08 2017 - 04:55:35 EST


>> > Voltage is limited to 3.3v and shared for all slots.
>> What voltage? The I/O voltage or the voltage for the card?
> From my understanding both, VMMC and VMMCQ are fixed at 3.3v.

Okay, then make sure to explicitly state that here.


>> > + if (bad_status(&rsp_sts))
>> > + req->cmd->error = -EILSEQ;
>> I don't think you should treat all errors as -EILSEQ. Please assign a
>> proper error code, depending on the error.
> Agreed, -ETIMEDOUT seems more appropriate for the timeouts. I'll go for
> -EIO for the dbuf_err (buffer space missing). What should I use for the
> CRC errors, -EILSEQ?

Yes, correct.


>> What does this really mean? Is this about HW support for better
>> dealing with data requests?
> Did David's reponse answer your questions?



>> > + /*
>> > + * Legacy platform doesn't support regulator but enables power gpio
>> > + * directly during platform probe.
>> > + */
>> > + if (host->global_pwr_gpiod)
>> > + /* Get a sane OCR mask for other parts of the MMC subsytem. */
>> > + return mmc_of_parse_voltage(dev->of_node, &mmc->ocr_avail);
>> Does really the legacy platforms use the mmc voltage range DT bindings!?
> The legacy DT's use (in the mmc slot nodes):
> voltage-ranges = <3300 3300>;
>> I would rather see that you assign a default value to mmc->ocr_avail,
>> than using this binding.
> The volatage seems to be identical for all legacy bindings I can find,
> so is it better to not parse it and use the 3.3 as default?

Yes, I think so.


>> > +union mio_emm_cmd {
>> > + u64 val;
>> > + struct mio_emm_cmd_s {
>> > +#ifdef __BIG_ENDIAN_BITFIELD
>> Huh. Sorry, but this is a big nack from me.
>> This isn't the common method for how we deal with endian issues in the
>> kernel. Please remove all use of the union types here and below. The
>> follow common patterns for how we deal with endian issues.
> May I ask why you dislike the bitfields? Or maybe it is easier when I
> explain why I decided to keep them:

My main concern is that is different compared to how we deal with
endian issues in the kernel.

I just don't like homebrewed hacks, but prefers sticking to defacto
standard methods.

> - One drawback of bitfields is poor performance on some architectures.
> That is not the case here, both MIPS64 and ARM64 have instructions
> capable of using bitfields without performance impact.
> - The used bitfield are all aligned to word size, usually the pattern in
> the driver is to readq / writeq the whole word (therefore the union
> val) and then set or read certain fields. That should avoid IMHO the
> unspecified behaviour the C standard mentions.
> - I prefer BIT_ULL and friends for single bits, but using macros for
> more then one bit is (again IMHO) much less readable then using
> bitfiels here. And all the endianess definitions are _only_ in the
> header file.
> Also, if I need to convert all of these I'll probably add some new bugs.
> What we have currently works fine on both MIPS and ARM64.

I understand that is will have an impact, however there are plenty of
good references in the kernel for how to do this.


Kind regards