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From: "H Hartley Sweeten" <hartleys@visionengravers.com>
To: "Mike Frysinger" <vapier.adi@gmail.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: Fri, 18 Sep 2009 19:00:13 -0400	[thread overview]
Message-ID: <BD79186B4FD85F4B8E60E381CAEE190901D41FB1@mi8nycmail19.Mi8.com> (raw)
In-Reply-To: <8bd0f97a0909171553s1b7ee725x728bbca2f49511a9@mail.gmail.com>

On Thursday, September 17, 2009 3:54 PM, Mike Frysinger wrote:
>> 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.

Actually you are breaking the mmc_spi driver.

By returning 0 when the methods are not supplied you are saying that the
master driver supports and locked the bus.  At a minimum, I think spi_lock_bus()
should return an error code if locking is not supported.

Also, as Andrew Morton pointed out, calling spi_unlock_bus() without having
a valid lock by calling spi_lock_bus() is a bug.

In addition your patch to mmc_spi should check the return code from
spi_lock_bus().  If the driver "requires" that the bus be locked it should
trigger an error path if it cannot be locked.

>> 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

Oiy... The lock/unlock functions are simple enough but the change needed
to bfin_spi_pump_messages() is a bit complicated.

What happens to next_msg if it is for other devices on the bus?

Regards,
Hartley

  reply	other threads:[~2009-09-18 23:00 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
2009-09-18 23:00     ` H Hartley Sweeten [this message]
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

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