Re: [PATCH 3/5] mmc: sdhi: Add write16_hook

Magnus Damm
2011-06-21T02:34:47Z

Hey Simon,

On Tue, Jun 21, 2011 at 11:09 AM, Simon Horman <horms@verge.net.au> wrote:
> On Tue, Jun 21, 2011 at 10:36:05AM +0900, Magnus Damm wrote:
>> On Tue, Jun 21, 2011 at 10:13 AM, Simon Horman <horms@verge.net.au> wrote:
>> > On Tue, Jun 21, 2011 at 09:59:37AM +0900, Magnus Damm wrote:
>> >> On Tue, Jun 21, 2011 at 9:50 AM, Simon Horman <horms@verge.net.au> wrote:
>> >> > On Tue, Jun 21, 2011 at 09:36:03AM +0900, Magnus Damm wrote:
>> >> >> On Tue, Jun 21, 2011 at 8:00 AM, Simon Horman <horms@verge.net.au> wrote:
>> >
>> > [snip]
>> >
>> >> >> > index 5a90266..0dc9804 100644
>> >> >> > --- a/include/linux/mfd/tmio.h
>> >> >> > +++ b/include/linux/mfd/tmio.h
>> >> >> > @@ -94,6 +101,7 @@ struct tmio_mmc_data {
>> >> >> >        void (*set_pwr)(struct platform_device *host, int state);
>> >> >> >        void (*set_clk_div)(struct platform_device *host, int state);
>> >> >> >        int (*get_cd)(struct platform_device *host);
>> >> >> > +       int (*write16_hook)(struct tmio_mmc_host *host, int addr);
>> >> >> >  };
>> >> >> >
>> >> >> >  static inline void tmio_mmc_cd_wakeup(struct tmio_mmc_data *pdata)
>> >> >>
>> >> >> What's the reason behind passing "struct tmio_mmc_host *"  as an
>> >> >> argument to the new hook? Performance? All other callbacks seem to
>> >> >> take a "struct platform_device *", so being consistent here may be
>> >> >> good unless it comes with too much overhead.
>> >> >
>> >> > The reason is that
>> >> > 1) The hook is called from sd_ctrl_write16 which takes
>> >> >   struct tmio_mmc_host * as its first argument and;
>> >> > 2) The hook that has been implemented calls sd_ctrl_read16() which takes a
>> >> >   struct tmio_mmc_host * as its first argument.
>> >> > So it seemed logical to pass that down.
>> >> >
>> >> > In the caes of 1) we can get the struct platform_device * using host->pdev.
>> >> > However, in the case of 2) is it less clear to me how we can get the
>> >> > struct tmio_mmc_host * from a struct platform_device *.
>> >>
>> >> Have a look at the code in tmio_mmc_host_suspend() for some code that
>> >> does struct device * -> struct tmio_mmc_host *:
>> >> int tmio_mmc_host_suspend(struct device *dev)
>> >> {
>> >>       struct mmc_host *mmc = dev_get_drvdata(dev);
>> >>       struct tmio_mmc_host *host = mmc_priv(mmc);
>> >>
>> >> You can easily change the dev_get_drvdata() to platform_get_drvdata(),
>> >> see include/linux/platform_device.h
>> >
>> > Thanks, I'm happy to make that change if you think it is worth it.
>> > (I will need to re-test on AG5, which I could do this afternoon
>> >  if it is free)
>>
>> Hm, perhaps it can be done with incremental patches in the future?
>>
>> I think it's good to be consistent and use the same argument passing
>> style as other callbacks, but at the same time I'm not 100% sure if
>> passing a platform data pointer is the best approach. It probably made
>> sense with the old tmio_mmc driver that only hooked up to MFD, but I'm
>> not sure if that's the case anymore. I'm sure there is room for plenty
>> of cleanups - but exactly what to do I don't know. =)
>>
>> At least passing a struct tmio_mmc_host * requires little conversion
>> which should add minimal overhead.
>
> Ok, lets stick with what we have for now.
> Its a fairly trivial change to update the arguments later
> if that is wanted. Testing is slightly less trivial
> due to availability of hardware, but not a major problem.
>
> Can you Acked-by, or Reviewed-by the patches in this series if
> you are now happy with them?

Sure, for all patches included in this series:
Acked-by: Magnus Damm <damm@opensource.se>

>> >> I guess a similar conversion can be done in tmio_mmc_enable_dma() to
>> >> move from writew() to sd_ctrl_write16()?
>> >
>> > Are you proposing changing tmio_mmc_enable_dma() to take
>> > a struct platform_device * as its first argument?
>>
>> No, not at all. I just recall someone pointing out that
>> tmio_mmc_enable_dma() skipped the tmio_mmc specific I/O routines and
>> used writew() directly. I suspected the reason behind this was the
>> difficulty of converting between different pointer types, but that may
>> not be true.
>
> I was probably the person who pointed that out to you.
> I'm unsure of the reason, but at least in its current form
> it appears not to be related to the parameters involved.

Yeah. Probably me being confused of which patches that modify which
functions. =)

>> > tmio_mmc_enable_dma() is already altered in one of the
>> > patches in this series to use sd_ctrl_write16() without
>> > altering the arguments taht tmio_mmc_enable_dma() takes.
>>
>> Ok, that's good.
>>
>> > static void tmio_mmc_enable_dma(struct tmio_mmc_host *host, bool enable)
>> > {
>> > #if defined(CONFIG_SUPERH) || defined(CONFIG_ARCH_SHMOBILE)
>> >        /* Switch DMA mode on or off - SuperH specific? */
>> >        sd_ctrl_write16(host, enable ? 2 : 0, CTL_DMA_ENABLE);
>> > #endif
>> > }
>>
>> Hm, perhaps it's my mail setup that's the issue, but the version of
>> "[PATCH 1/5] mmc: tmio: name 0xd8 as CTL_DMA_ENABLE" that I'm looking
>> at is still using writew().
>
> The writew() -> sd_ctrl_write16() change is made by the following patch
> in the series, "[PATCH 2/5] mmc: tmio: Share register access functions".
>
> The last hunk looks like this:
>
> diff --git a/drivers/mmc/host/tmio_mmc_dma.c
> b/drivers/mmc/host/tmio_mmc_dma.c
> index 9c4da66..f24a029 100644
> --- a/drivers/mmc/host/tmio_mmc_dma.c
> +++ b/drivers/mmc/host/tmio_mmc_dma.c
> @@ -26,7 +26,7 @@ static void tmio_mmc_enable_dma(struct tmio_mmc_host *host, bool enable)
>  {
>  #if defined(CONFIG_SUPERH) || defined(CONFIG_ARCH_SHMOBILE)
>        /* Switch DMA mode on or off - SuperH specific? */
> -       writew(enable ? 2 : 0, host->ctl + (CTL_DMA_ENABLE << host->bus_shift));
> +       sd_ctrl_write16(host, enable ? 2 : 0, CTL_DMA_ENABLE);
>  #endif
>  }

Gotcha. Looking good, thank you!

/ magnus