linux-kernel - Re: [PATCH 3/4] atmel-mci: support multiple mmc slots

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Date:	Tue, 23 Sep 2008 20:16:50 +0200
From:	Haavard Skinnemoen <haavard.skinnemoen@...el.com>
To:	Pierre Ossman <drzeus-list@...eus.cx>
Cc:	kernel@...32linux.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] atmel-mci: support multiple mmc slots

Pierre Ossman <drzeus-list@...eus.cx> wrote:
> On Mon, 22 Sep 2008 18:38:16 +0200
> Haavard Skinnemoen <haavard.skinnemoen@...el.com> wrote:
> 
> > The Atmel MCI controller can drive multiple cards through separate sets
> > of pins, but only one at a time. This patch adds support for
> > multiplexing access to the controller so that multiple card slots can be
> > used as if they were hooked up to separate mmc controllers.
> > 
> 
> This multiplexing shenanigans seems to be all the rage these days...

Apparently. I suppose it saves a few gates.

> >  
> >  static void atmci_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
> >  {
> > -	struct atmel_mci	*host = mmc_priv(mmc);
> > +	struct atmel_mci_slot	*slot = mmc_priv(mmc);
> > +	struct atmel_mci	*host = slot->host;
> >  
> >  	if (ios->clock) {
> >  		u32 clkdiv;
> 
> You forgot the most important part; how to handle the clock given two
> different requests.

I don't think I did. The set_ios() function merely calculates the value
of MR and stashes it away. It isn't written to the controller until
after the host has been claimed for a request.

> (This will also get a bit more painful when/if the core starts
> disabling the clock when a card is idle)

The atmel-mci driver already stops the clock between requests. Though I
don't understand why the core would care about clocks.

> > +
> > +	if (gpio_is_valid(slot->detect_pin)) {
> > +		int ret;
> > +
> > +		setup_timer(&slot->detect_timer, atmci_detect_change,
> > +				(unsigned long)slot);
> > +
> > +		ret = request_irq(gpio_to_irq(slot->detect_pin),
> > +				atmci_detect_interrupt,
> > +				IRQF_TRIGGER_FALLING | IRQF_TRIGGER_RISING,
> > +				"mmc-detect", slot);
> > +		if (ret) {
> > +			dev_dbg(&mmc->class_dev,
> > +				"could not request IRQ %d for detect pin\n",
> > +				gpio_to_irq(slot->detect_pin));
> > +			gpio_free(slot->detect_pin);
> > +			slot->detect_pin = -EBUSY;
> > +		}
> > +	}
> 
> Fall back to polling?

Probably, yes. Can I fall back to polling after the host has been
registered?

> > +	/* We need at least one slot to succeed */
> > +	ret = -1;
> > +	if (pdata->slot[0].bus_width)
> > +		ret &= atmci_init_slot(host, &pdata->slot[0],
> > +				MCI_SDCSEL_SLOT_A);
> > +	if (pdata->slot[1].bus_width)
> > +		ret &= atmci_init_slot(host, &pdata->slot[1],
> > +				MCI_SDCSEL_SLOT_B);
> > +	if (ret) {
> > +		ret = -ENODEV;
> > +		goto err_init_slot;
> >  	}
> 
> Memory/resource leak.

Hmm...I guess I was being too clever. I'll redo it with less clever
code.

Haavard
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