Messages in this thread | | | Subject | Re: [PATCH 1/2] spi: new SPI bus lock/unlock functions | From | Li Yi <> | Date | Mon, 21 Sep 2009 14:33:00 +0800 |
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On Fri, 2009-09-18 at 14:29 -0700, Andrew Morton wrote: > On Thu, 17 Sep 2009 18:03:16 -0400 > Mike Frysinger <vapier@gentoo.org> 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. > > > > Signed-off-by: Yi Li <yi.li@analog.com> > > Signed-off-by: Bryan Wu <cooloney@kernel.org> > > Signed-off-by: Mike Frysinger <vapier@gentoo.org> > > --- > > Andrew: we've posted these in the past with no response. could you pick > > them up please ? > > > > drivers/spi/spi.c | 48 +++++++++++++++++++++++++++++++++++++++++++++++ > > include/linux/spi/spi.h | 7 ++++++ > > 2 files changed, 55 insertions(+), 0 deletions(-) > > > > diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c > > index 70845cc..b82b8ad 100644 > > --- a/drivers/spi/spi.c > > +++ b/drivers/spi/spi.c > > @@ -653,6 +653,54 @@ static void spi_complete(void *arg) > > } > > > > /** > > + * 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. > > Hence spi_lock_bus() basically has to use a spinning lock? > > So code which has called spi_lock_bus() cannot sleep until it calls > spi_unlock_bus()? > > That's worth mentioning in the description. > Code called spi_lock_bus() _can_ sleep. This is mentioned in the comments.
> > + * 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. > > That's crazy. > > Calling spi_unlock_bus() without having earlier called spi_lock_bus() > is a bug, and the kernel's response should be to go BUG(), not to > silently ignore the bug. Especially as the implementation will need to > add extra code to silently ignore the bug! > I will change the patch to fix this. Thanks.
> Perhaps the comment wasn't well thought-out. I cannot tell because I > cannot see any implementations of ->lock_bus() anywhere. > The implementation for blackfin spi master is in drivers/spi/spi_bfin5xx.c: http://git.kernel.org/?p=linux/kernel/git/vapier/blackfin.git;a=commitdiff;h=cc54fa8ed63e11a000031bc650d41d57b441803d
As you mentioned, if a spi device calls spi_unlock_bus() without calling spi_lock_bus() before, it should be returned an error. This will be fixed in next version of the patch.
-Yi
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