Date:	Sun, 1 Feb 2009 19:54:35 +0100
From:	Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:	Pierre Ossman <drzeus-mmc@...eus.cx>, linux-kernel@...r.kernel.org,
	Alex Dubov <oakad@...oo.com>
Subject: Re: RFC: Driver for CB710/720 memory card reader (MMC part) - v3

Hello again,

Sorry for a long delay with my reply.

On Fri, Nov 14, 2008 at 10:06:58PM +0100, Pierre Ossman wrote:
> On Wed, 29 Oct 2008 15:11:47 +0100
> Michał Mirosław <mirq-linux@...e.qmqm.pl> wrote:
> > Here is the driver for CB710 SD/MMC reader updated to recently released
> > kernel version 2.6.27. The code is divided into PCI device driver
> > (wrapped that registers three platform devices) and MMC reader driver.
> > This idea was taken from TIFM driver.
> > 
> > Changes from v2:
> >  - return EINVAL for unsupported data transfer sizes
> >  - use sg_mapping_iter for PIO from/to scatterlist
> >  - add slot release function and prevent kobject leak on device registration's
> >    error path
> > 
> > If this code looks reasonably good, then I'll post patches against the
> > real kernel tree. The file distribution plan is:
> It looks more or less good to go. I have some small notes, and you
> probably need to poke some scatterlist folks to okay those changes
> (should probably be a separate patch).

There's no entry in MAINTAINERS list, but I assume it's Jens Axboe as he's
in the copyright section in scatterlist.c.

> > +/* slot port accessors - in case it turns out inX() is all that is needed */
> > +#define CB710_PORT_ACCESSORS(t) \
> > +static inline void cb710_write_port_##t(struct cb710_slot *slot,	\
> > +	unsigned port, u##t value)					\
> > +{									\
> > +	iowrite##t(value, slot->iobase + port);				\
> > +}									\
> > +									\
> > +static inline u##t cb710_read_port_##t(struct cb710_slot *slot,		\
> > +	unsigned port)							\
> > +{									\
> > +	return ioread##t(slot->iobase + port);				\
> > +}									\
> > +									\
> > +static inline void cb710_modify_port_##t(struct cb710_slot *slot,	\
> > +	unsigned port, u##t set, u##t clear)				\
> > +{									\
> > +	iowrite##t(							\
> > +		(ioread##t(slot->iobase + port) & ~clear)|set,		\
> > +		slot->iobase + port);					\
> > +}
> > +
> > +CB710_PORT_ACCESSORS(8)
> > +CB710_PORT_ACCESSORS(16)
> > +CB710_PORT_ACCESSORS(32)
> This is clearer than what you had before, but I still think you should
> consider using the kernel functions directly.

The really useful one here is cb710_modify_port_*(), read/write are for
consistency. I'd prefer to keep those wrappers because they help to eliminate
some noise from register access logic in the driver.

> > +/* helper functions */
> > +
> > +static inline void cb710_set_irq_handler(struct cb710_slot *slot,
> > +	cb710_irq_handler_t handler)
> > +{
> > +	rcu_assign_pointer(slot->irq_handler, handler);
> > +	synchronize_rcu();	/* sync to IRQ handler */
> > +}
> Why RCU:s? This smells of premature optimisation.

I thought this as the easiest way to assure that on return from
cb710_set_irq_handler() there's no interrupt handler running using the
old slot->irq_handler value.

> > +/* per-MMC-reader structure */
> > +struct cb710_mmc_reader {
> > +	struct tasklet_struct finish_req_tasklet;
> > +	struct mmc_request *mrq;
> > +	spinlock_t irq_lock;
> > +	unsigned char last_power_mode;
> > +#ifdef VERBOSE_DEBUG
> > +	spinlock_t serialization_lock;
> > +	unsigned char active_req, active_ios;
> > +#endif
> > +};
> I couldn't find VERBOSE_DEBUG defined somewhere. For ease of use with
> future testers, you should connect it to some Kconfig option.

This is mostly related to veryfying some assumptions on the MMC core
infrastructure. I can remove this altogether if the calls to driver
->request() and ->set_ios() are really guaranteed to be serialized.

> > +static int cb710_suspend(struct pci_dev *pdev, pm_message_t state)
> > +{
> > +	pci_save_state(pdev);
> > +	pci_disable_device(pdev);
> > +	if (state.event & PM_EVENT_SLEEP)
> > +		pci_set_power_state(pdev, PCI_D3cold);
> > +	return 0;
> > +}
> > +
> > +static int cb710_resume(struct pci_dev *pdev)
> > +{
> > +	pci_set_power_state(pdev, PCI_D0);
> > +	pci_restore_state(pdev);
> > +	return pcim_enable_device(pdev);
> > +}
> Free/restore interrupt?

Hmm. I checked couple random drivers in kernel tree and none (including
MMC host drivers) are touching interrupt allocation in suspend/resume.

> > +#if 0
> > +	/* original driver set bit 14 for MMC/SD application
> > +	 * commands. There's no difference 'on the wire' and
> > +	 * it apparently works without it anyway.
> > +	 */
> > +	if (flags & MMC_CMD_IS_APPCMD)
> > +		cb_flags |= 0x4000;
> > +#endif
> As this code is just useless, please clean it out before you submit the
> driver.

Will turn this into pure comment - just to remember.

> > +	mmc->ops = &cb710_mmc_host;
> > +	mmc->f_max = val;
> > +	mmc->f_min = val >> cb710_clock_divider_log2[CB710_MAX_DIVIDER_IDX];
> > +	mmc->ocr_avail = MMC_VDD_32_33|MMC_VDD_33_34|MMC_VDD_34_35;
> Since you can't change the voltage, this seems wrong. My guess is that
> the MMC_VDD_34_35 define should go.

That's what the original driver advertises. I can't verify the exact
voltage that is supplied to the card, so I'll assume that's 3.3V and
remove MMC_VDD_34_35 as you suggest.

> > +static int __devexit cb710_mmc_exit(struct platform_device *pdev)
> > +{
> > +	struct cb710_slot *slot = cb710_pdev_to_slot(pdev);
> > +	struct mmc_host *mmc = cb710_slot_to_mmc(slot);
> > +	struct cb710_mmc_reader *reader = mmc_priv(mmc);
> > +
> > +	mmc_remove_host(mmc);
> > +
> > +	/* XXX what if IRQ arrives now? */
> 
> Most drivers handle this by sticking their head in the sand, but the
> proper way is probably to disable the card insertions interrupt before
> mmc_remove_host().
> (and there should be no other unsolicited interrupts)

Will try.

Best Regards,
Michał Mirosław

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