linux-kernel - Re: [PATCH] mmc: Fix read-only detection with JMicron 388 chip

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Date:	Thu, 21 Apr 2011 19:09:36 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Chris Ball <cjb@...top.org>
Cc:	Aries Lee <arieslee@...cron.com>, linux-mmc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mmc: Fix read-only detection with JMicron 388 chip

At Thu, 21 Apr 2011 12:40:26 -0400,
Chris Ball wrote:
> 
> Hi Takashi,
> 
> On Thu, Apr 21 2011, Takashi Iwai wrote:
> > On HP laptops with JMicron 388 chip, the write-locked SD card isn't
> > detected correctly as read-only in many cases.  This is because the
> > PRESENT_STATE register becomes unsable just after plugging, and it
> > returns the WRITE_PROTECT bit wrongly at the first read.
> >
> > This patch fixes the read-only detection by adding the own get_ro op
> > for checking the register more intensively with a relatively long
> > delay.
> >
> > The patch is tested with 2.6.39-rc4 kernel.
> >
> > Cc: Aries Lee <arieslee@...cron.com>
> > Signed-off-by: Takashi Iwai <tiwai@...e.de>
> > ---
> >  drivers/mmc/host/sdhci-pci.c |   34 ++++++++++++++++++++++++++++++++++
> >  1 files changed, 34 insertions(+), 0 deletions(-)
> >
> > diff --git a/drivers/mmc/host/sdhci-pci.c b/drivers/mmc/host/sdhci-pci.c
> > index a136be7..9037b2a 100644
> > --- a/drivers/mmc/host/sdhci-pci.c
> > +++ b/drivers/mmc/host/sdhci-pci.c
> > @@ -346,6 +346,35 @@ static void jmicron_enable_mmc(struct sdhci_host *host, int on)
> >  	writeb(scratch, host->ioaddr + 0xC0);
> >  }
> >  
> > +/* As PRESENT_STATE register becomes unstable just after plugging,
> > + * need to check the RO-cap multiple times with a relatively long delay.
> > + */
> > +
> > +#define SAMPLE_COUNT	5
> > +
> > +static unsigned int jmicron_get_ro(struct sdhci_host *host)
> > +{
> > +	int i, ro_count;
> > +
> > +	ro_count = 0;
> > +	for (i = 0; i < SAMPLE_COUNT; i++) {
> > +		int present = sdhci_readl(host, SDHCI_PRESENT_STATE);
> > +		if (!(present & SDHCI_WRITE_PROTECT)) {
> > +			if (++ro_count > SAMPLE_COUNT / 2)
> > +				return 1;
> > +		}
> > +		msleep(30);
> > +	}
> > +	return 0;
> > +}
> > +
> > +static int sdhci_pci_enable_dma(struct sdhci_host *host);
> > +
> > +static struct sdhci_ops jmicron_pci_ops = {
> > +	.enable_dma	= sdhci_pci_enable_dma,
> > +	.get_ro		= jmicron_get_ro,
> > +};
> > +
> >  static int jmicron_probe_slot(struct sdhci_pci_slot *slot)
> >  {
> >  	if (slot->chip->pdev->revision == 0) {
> > @@ -383,6 +412,11 @@ static int jmicron_probe_slot(struct sdhci_pci_slot *slot)
> >  
> >  	slot->host->mmc->caps |= MMC_CAP_BUS_WIDTH_TEST;
> >  
> > +	/* Replace the ops for unstable get_ro detection */
> > +	if (slot->chip->pdev->device == PCI_DEVICE_ID_JMICRON_JMB388_SD ||
> > +	    slot->chip->pdev->device == PCI_DEVICE_ID_JMICRON_JMB388_ESD)
> > +		slot->host->ops = &jmicron_pci_ops;
> > +
> >  	return 0;
> >  }
> 
> I don't like overwriting ops here -- it's too magical, and now we have
> to maintain the ops table in two places.  A quirk seems justified here,
> even though we're trying to reduce them in general.

Well, I also used quirk bit in my very first version I worked for
2.6.32 kernel.  But when I looked at 2.6.39, quirks are almost full --
only the last one bit is left for bit 31.  So I didn't want to finish
it :)

>  Can anyone find a better solution?
 
One way would be to copy the ops table itself in struct sdhci_host
instead of keeping the ops table pointer.  Then you can overwrite only
the specific op in each probe_slot callback.


thanks,

Takashi
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