Messages in this thread | | | Subject | RE: [spi-devel-general] [PATCH 1/2] spi: new SPI bus lock/unlockfunctions | Date | Thu, 17 Sep 2009 18:45:54 -0400 | From | "H Hartley Sweeten" <> |
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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. > > 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 ?
Hello Mike,
This is the first time I have seen this patch. I might have missed it previously.
I would like to test it on my ep93xx system but have some question below.
> 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. > + * > + * 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. 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.
Also, do you have a master driver that does have the {lock/unlock}_bus methods? I would like to see how you handled it.
Regards, Hartley
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