lkml.org 
[lkml]   [2022]   [Jan]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v6 3/3] mmc: Add driver for LiteX's LiteSDCard interface
Hi Andy,

Thanks again, replies and follow-up questions inline below:

On Thu, Jan 06, 2022 at 08:19:39PM +0200, Andy Shevchenko wrote:
> On Thu, Jan 6, 2022 at 7:48 PM Gabriel Somlo <gsomlo@gmail.com> wrote:
> >
> > LiteX (https://github.com/enjoy-digital/litex) is a SoC framework
> > that targets FPGAs. LiteSDCard is a small footprint, configurable
> > SDCard core commonly used in LiteX designs.
> >
> > The driver was first written in May 2020 and has been maintained
> > cooperatively by the LiteX community. Thanks to all contributors!
>
> > +config MMC_LITEX
> > + tristate "LiteX MMC Host Controller support"
> > + depends on OF
> > + depends on PPC_MICROWATT || LITEX || COMPILE_TEST
> > + help
> > + This selects support for the MMC Host Controller found in LiteX SoCs.
> > +
> > + If unsure, say N.
>
> What would be the module name if built as a module?

litex_mmc.ko -- why are you asking? I.e., should I mention that anywhere
in the Kconfig blurb (I don't see other blurbs doing that, fwiw)?

> ...
>
> > +/*
> > + * LiteX LiteSDCard driver
> > + *
> > + * Copyright (C) 2019-2020 Antmicro <contact@antmicro.com>
> > + * Copyright (C) 2019-2020 Kamil Rakoczy <krakoczy@antmicro.com>
> > + * Copyright (C) 2019-2020 Maciej Dudek <mdudek@internships.antmicro.com>
> > + * Copyright (C) 2020 Paul Mackerras <paulus@ozlabs.org>
> > + * Copyright (C) 2020-2021 Gabriel Somlo <gsomlo@gmail.com>
>
> > + *
>
> Redundant blank line.

OK, removed.

>
> > + */
>
> ...
>
> > +#include <linux/module.h>
> > +#include <linux/litex.h>
> > +#include <linux/of.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/clk.h>
> > +#include <linux/interrupt.h>
> > +#include <linux/iopoll.h>
> > +#include <linux/mmc/sd.h>
> > +#include <linux/mmc/mmc.h>
> > +#include <linux/mmc/host.h>
> > +#include <linux/delay.h>
> > +#include <linux/dma-mapping.h>
>
> Perhaps keep it sorted?

OK, sorted. Now looks like this:

#include <linux/clk.h>
#include <linux/delay.h>
#include <linux/dma-mapping.h>
#include <linux/interrupt.h>
#include <linux/iopoll.h>
#include <linux/litex.h>
#include <linux/module.h>
#include <linux/mmc/host.h>
#include <linux/mmc/mmc.h>
#include <linux/mmc/sd.h>
#include <linux/mmc/slot-gpio.h>
#include <linux/of.h>
#include <linux/platform_device.h>

> It will easily show, for example, absence of bits.h.

I'm not getting any errors or warnings re. missing bits.h -- why are
you mentioning it explicitly? (for the record, I try not to explicitly
include anything unless I absolutely have to, so I try to avoid
including headers included via other headers I already *have* to
include explicitly!)

I'm expecting you're going to tell me that's wrong, but then I'm much
less confident of a clean canonical way of determining exactly what
headers must be mentioned explicitly in a driver -- please advise! :)

>
> > + ret = readx_poll_timeout(litex_read8, reg, evt, (evt & SD_BIT_DONE),
>
> Too many parentheses.

OK, removed (from both occurrences of `readx_poll_timeout()`).

>
> > + SD_SLEEP_US, SD_TIMEOUT_US);
>
> > + if (ret || (evt & SD_BIT_TIMEOUT))
>
> Redundant second condition. If you want +1 iteration, increase timeout.

Well, readx_poll_timeout() returns -ETIMEDOUT or 0, depending on whether
or not it read the SD_BIT_DONE bit from the provided register reg.
But even if it did return 0, the hardware might have returned its own
timeout flag (SD_BIT_TIMEOUT) before readx_poll_timeout() decided to
give up on polling the register. So we can time out in one of two
different ways, and we need to check for both.

> > + return -ETIMEDOUT;
>
> Why shadowed error code?

See above -- if readx_poll_timeout returned 0, we should still return
-ETIMEDOUT in case the hardware set the SD_BIT_TIMEOUT flag. I figured
I'd deal with all timeout scenarios in one place, but we can definitely
split that out to avoid confusion, something like this:

...
ret = readx_poll_timeout(litex_read8, reg, evt, evt & SD_BIT_DONE,
SD_SLEEP_US, SD_TIMEOUT_US);
if (ret)
return ret;
if (evt == SD_BIT_DONE)
return 0;
if (evt & SD_BIT_WR_ERR)
return -EIO;
if (evt & SD_BIT_TIMEOUT) // <<< HERE
return -ETIMEDOUT;
if (evt & SD_BIT_CRC_ERR)
return -EILSEQ;
...

> ...
>
> > + pr_err("%s: unknown error evt=%x\n", __func__, evt);
>
> Use dev_err().

OK, done.

> ...
>
> > + /* Wait for an interrupt if we have an interrupt and either there is
> > + * data to be transferred, or if the card can report busy via DAT0.
> > + */
>
> This comment style is for the net subsystem, for others we use
> /*
> * Starting here...
> */
>
> Fix it everywhere in your code.

OK, multi-line comment style updated across the entire file.

> ...
>
> > + reg = host->sdcore + LITEX_CORE_CMDRSP;
> > + for (i = 0; i < 4; i++) {
> > + host->resp[i] = litex_read32(reg);
> > + reg += sizeof(u32);
> > + }
>
> Isn't it memcpy_fromio()?

Yes, that appears to be the case. Looking at `litex_read32()`
(in include/linux/litex.h), it's defined as

le32_to_cpu((__le32 __force)readl(addr))

which counts as a "__raw_readl()", i.e., without the byteswap occurring
on BE architectures. It looks like memcpy_fromio() doesn't play byteswap
games on BE either, so they should be equivalent. With the caveat that
I only have the ability to test on LE!

For now, based on the above observations, I think it's safe to use
memcpy_fromio() here.

> ...
>
> > + if (!host->app_cmd && cmd == SD_SEND_RELATIVE_ADDR)
> > + host->rca = (host->resp[3] >> 16) & 0xffff;
>
> Are you expecting a 32-bit value to be bigger than 2^32-1?

Fair enough :)

> ...
>
> > + div = min(max(div, 2U), 256U);
>
> clamp_t() / clamp_val() ?

OK, changed to `div = clamp_val(div, 2U, 256U);`

> ...
>
> > + ret = platform_get_irq_optional(host->dev, 0);
> > + if (ret == -ENXIO || ret == 0) {
> > + dev_warn(dev, "Failed to get IRQ, using polling\n");
> > + goto use_polling;
> > + }
> > + if (ret < 0)
> > + return ret; /* e.g., deferred probe */
> > + host->irq = ret;
>
> Can it be rather written as
>
> ret = platform_get_irq_optional(host->dev, 0);
> if (ret < 0 && ret != -ENXIO)
> return ret;
> if (ret > 0)
> host->irq = ret;
> else {
> dev_warn(dev, "Failed to get IRQ, using polling\n");
> goto use_polling;
> }
>
> ?

OK, done.

> ...
>
> > +use_polling:
> > + host->mmc->caps |= MMC_CAP_NEEDS_POLL;
>
> > + host->irq = 0;
>
> Isn't it 0 by default?

Yes, because of kzalloc() by way of mmc_alloc_host(). So I don't have to
set it to 0 explicitly -- Done.

> ...
>
> > + mmc = mmc_alloc_host(sizeof(struct litex_mmc_host), &pdev->dev);
>
> > + /* NOTE: defaults to max_[req,seg]_size=PAGE_SIZE, max_blk_size=512,
> > + * and max_blk_count accordingly set to 8;
> > + * If for some reason we need to modify max_blk_count, we must also
> > + * re-calculate `max_[req,seg]_size = max_blk_size * max_blk_count;`
> > + */
>
> Can you rather not split code by this comment. It makes sense to be above, no?

OK -- Done.

> > + if (!mmc)
> > + return -ENOMEM;
>
> ...
>
> > + /* set default sd_clk frequency range based on empirical observations
> > + * of LiteSDCard gateware behavior on typical SDCard media
> > + */
>
> Start sentences from capital letters and keep proper style of
> multi-line comments.

Multi-line comment style fixed per your earlier observation.

I also went and capitalized the first letter of each comment throughout
the source.

> ...
>
> > +err:
> > + mmc_free_host(mmc);
> > + return ret;
>
> This...
>
> > +}
> > +
> > +static int litex_mmc_remove(struct platform_device *pdev)
> > +{
> > + struct litex_mmc_host *host = dev_get_drvdata(&pdev->dev);
> > +
> > + if (host->irq > 0)
> > + free_irq(host->irq, host->mmc);
> > + mmc_remove_host(host->mmc);
> > + mmc_free_host(host->mmc);
>
> ...and this have ordering issues. You mixed devm_*() with non-devm_*()
> APIs in the wrong way.
>
> Also, I haven't noticed the free_irq() call in the error path of
> ->probe(). Isn't it missed?

OK, I've reordered everything (and added the missing free_irq() call
like so:

static int litex_mmc_probe(struct platform_device *pdev)
{
...
...
return 0;

err:
if (host->irq > 0)
free_irq(host->irq, host->mmc);
mmc_free_host(mmc);
return ret;
}

static int litex_mmc_remove(struct platform_device *pdev)
{
struct litex_mmc_host *host = dev_get_drvdata(&pdev->dev);

mmc_remove_host(host->mmc);
if (host->irq > 0)
free_irq(host->irq, host->mmc);
mmc_free_host(host->mmc);

return 0;
}

Looking at other examples in drivers/mmc/host/* I'm not sure if/what
other ordering issues or devm/non-devm mixing violations I'm
perpetrating: if there are any left, could you please point them out
in a bit more detail?

> > + return 0;
> > +}
>
> ...
>
> > + .of_match_table = of_match_ptr(litex_match),
>
> Wrong usage of of_match_ptr().

Huh? It's consistent with how a whole bunch of other files in
drivers/mmc/host/*.c are using it, can you please elaborate?

Thanks much for taking the time to review the driver, much appreciated!
I'll send out a v7 as soon as I get some clarity on the portions above
that I'm still confused about... :)

Thanks again,
--Gabriel

\
 
 \ /
  Last update: 2022-01-06 23:51    [W:0.078 / U:0.084 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site