linux-spi.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Mike Frysinger <vapier.adi@gmail.com>
To: H Hartley Sweeten <hartleys@visionengravers.com>
Cc: spi-devel-general@lists.sourceforge.net,
	David Brownell <dbrownell@users.sourceforge.net>,
	Yi Li <yi.li@analog.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [spi-devel-general] [PATCH 1/2] spi: new SPI bus lock/unlockfunctions
Date: Thu, 17 Sep 2009 18:53:58 -0400	[thread overview]
Message-ID: <8bd0f97a0909171553s1b7ee725x728bbca2f49511a9@mail.gmail.com> (raw)
In-Reply-To: <BD79186B4FD85F4B8E60E381CAEE190901D41E44@mi8nycmail19.Mi8.com>

On Thu, Sep 17, 2009 at 18:45, H Hartley Sweeten wrote:
> On Thursday, September 17, 2009 3:03 PM, Mike Frysinger wrote:
>> From: Yi Li <yi.li@analog.com>
>>
>> For some MMC cards over SPI bus, it needs to lock the SPI bus for its own
>> use.  The SPI transfer must not be interrupted by other SPI devices that
>> share the SPI bus with SPI MMC card.
>>
>> This patch introduces 2 APIs for SPI bus locking operation.
>>
>>  /**
>> + * spi_lock_bus - lock SPI bus for exclusive access
>> + * @spi: device which want to lock the bus
>> + * Context: any
>> + *
>> + * Once the caller owns exclusive access to the SPI bus,
>> + * only messages for this device will be transferred.
>> + * Messages for other devices are queued but not transferred until
>> + * the bus owner unlock the bus.
>> + *
>> + * The caller may call spi_lock_bus() before spi_sync() or spi_async().
>> + * So this call may be used in irq and other contexts which can't sleep,
>> + * as well as from task contexts which can sleep.
>> + *
>> + * It returns zero on success, else a negative error code.
>> + */
>> +int spi_lock_bus(struct spi_device *spi)
>> +{
>> +     if (spi->master->lock_bus)
>> +             return spi->master->lock_bus(spi);
>> +     else
>> +             return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(spi_lock_bus);
>> +
>> +/**
>> + * spi_unlock_bus - unlock SPI bus
>> + * @spi: device which want to unlock the bus
>> + * Context: any
>> + *
>> + * The caller has called spi_lock_bus() to lock the bus. It calls
>> + * spi_unlock_bus() to release the bus so messages for other devices
>> + * can be transferred.
>> + *
>> + * If the caller did not call spi_lock_bus() before, spi_unlock_bus()
>> + * should have no effect.
>> + *
>> + * It returns zero on success, else a negative error code.
>> + */
>> +int spi_unlock_bus(struct spi_device *spi)
>> +{
>> +     if (spi->master->unlock_bus)
>> +             return spi->master->unlock_bus(spi);
>> +     else
>> +             return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(spi_unlock_bus);
>> +
>> +/**
>
> I assume the spi master driver must supply the {lock/unlock}_bus methods
> to properly support the locking.

currently, yes.  a common solution would be nice.  ideas/patches welcome ;).

> But, by returning 0 when the methods
> are not supplied you are basically saying all the current master drivers
> in mainline support bus locking.  I think this is really only "true" if
> spi->master->num_chipselect == 1.

right, but that is no different from what we have today.  there is no
way for a client to guarantee exclusive access, so you cant write code
assuming it in the first place.  the only consumer thus far (mmc_spi)
actually errors out if such conditions exist.

in other words, we arent breaking anything.

> Also, do you have a master driver that does have the {lock/unlock}_bus
> methods?  I would like to see how you handled it.

http://git.kernel.org/?p=linux/kernel/git/vapier/blackfin.git;a=commitdiff;h=cc54fa8ed63e11a000031bc650d41d57b441803d
-mike

  reply	other threads:[~2009-09-17 22:53 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-09-17 22:03 [PATCH 1/2] spi: new SPI bus lock/unlock functions Mike Frysinger
2009-09-17 22:03 ` [PATCH 2/2] mmc_spi: lock the SPI bus when accessing the card Mike Frysinger
2009-09-18  0:29   ` [spi-devel-general] [PATCH 2/2] mmc_spi: lock the SPI bus whenaccessing " H Hartley Sweeten
2009-09-18  0:52     ` [PATCH 2/2 v2] mmc_spi: lock the SPI bus when accessing " Mike Frysinger
2009-09-18 21:30       ` Andrew Morton
2009-09-17 22:45 ` [spi-devel-general] [PATCH 1/2] spi: new SPI bus lock/unlockfunctions H Hartley Sweeten
2009-09-17 22:53   ` Mike Frysinger [this message]
2009-09-18 23:00     ` H Hartley Sweeten
2009-09-19 19:11       ` Mike Frysinger
2009-09-21  8:08       ` Li Yi
2009-09-18 21:29 ` [PATCH 1/2] spi: new SPI bus lock/unlock functions Andrew Morton
2009-09-21  6:33   ` Li Yi
2009-09-21 13:36     ` Mike Frysinger
2009-09-22 14:15 ` Mike Frysinger
2009-12-16 22:49 ` [spi-devel-general] [PATCH 1/2] spi: new SPI bus lock/unlockfunctions H Hartley Sweeten
2009-12-16 23:00   ` Mike Frysinger

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=8bd0f97a0909171553s1b7ee725x728bbca2f49511a9@mail.gmail.com \
    --to=vapier.adi@gmail.com \
    --cc=akpm@linux-foundation.org \
    --cc=dbrownell@users.sourceforge.net \
    --cc=hartleys@visionengravers.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=spi-devel-general@lists.sourceforge.net \
    --cc=yi.li@analog.com \
    --subject='Re: [spi-devel-general] [PATCH 1/2] spi: new SPI bus lock/unlockfunctions' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).