From mboxrd@z Thu Jan 1 00:00:00 1970 From: Grant Likely Subject: Re: [PATCH 1/5] spi: spi_lock_bus and spi_unlock_bus Date: Tue, 16 Feb 2010 13:43:59 -0700 Message-ID: References: <20100216204450.e043eed8.eschwab@online.de> <20100216205720.ebe949a1.eschwab@online.de> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Cc: David Brownell , vapier-aBrp7R+bbdUdnm+yROfE0A@public.gmane.org, spi-devel-general-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, yi.li-OyLXuOCK7orQT0dZR+AlfA@public.gmane.org To: Ernst Schwab Return-path: In-Reply-To: <20100216205720.ebe949a1.eschwab-BGeptl67XyCzQB+pC5nmwQ@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: spi-devel-general-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: linux-spi.vger.kernel.org On Tue, Feb 16, 2010 at 12:57 PM, Ernst Schwab wrote: > From: Yi Li > > For some MMC cards over SPI bus, it needs to lock the SPI bus for its own > use. =A0The 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 > Signed-off-by: Bryan Wu > Signed-off-by: Mike Frysinger > --- > Andrew: we've posted these in the past with no response. =A0could you pick > =A0 =A0 =A0 =A0them up please ? > =A0drivers/spi/spi.c =A0 =A0 =A0 | =A0 48 +++++++++++++++++++++++++++++++= ++++++++++++++++ > =A0include/linux/spi/spi.h | =A0 =A07 ++++++ > =A02 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) > =A0} > > =A0/** > + * 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) > +{ > + =A0 =A0 =A0 if (spi->master->lock_bus) > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 return spi->master->lock_bus(spi); > + =A0 =A0 =A0 else > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 return 0; > +} > +EXPORT_SYMBOL_GPL(spi_lock_bus); This series seems to try and solve the problem the hard way, and by creating a new locking scheme (and as history shows, new locking schemes are *alwasy* broken). Why is the locking getting pushed down to the bus driver level? It seems to me that the whole thing could be handled with common code and a mutex in the spi_master structure. spi_sync would be easy to handle by putting a mutex around the spi_message submission. spi_async would be a little harder since it needs to be atomic, but that could also be handled with a flag protected by a spinlock. Basically, the idea is that existing drivers continue to use the API as-is Drivers that want to lock the bus for exclusive access must call spi_lock_bus() which should take the mutex and then sleep until all in-flight spi_messages are processed. After that, anyone calling spi_async() will simply sleep until the locker unlocks the bus again. To handle spi_sync() would probably require a flag protected by a spinlock. If the flag is set, then spi_sync() would simply fail. Finally, the locking driver would need locked versions of spi_sync() and spi_async() that sidestep the lock checks. It would only be valid to call these versions when holding the SPI bus lock. There is no need to specify the spi_device in the lock request. Since the lock is exclusive, it is known that the only driver calling the locked API version must already hold the lock. Have I got this wrong? g. > + > +/** > + * 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) > +{ > + =A0 =A0 =A0 if (spi->master->unlock_bus) > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 return spi->master->unlock_bus(spi); > + =A0 =A0 =A0 else > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 return 0; > +} > +EXPORT_SYMBOL_GPL(spi_unlock_bus); > + > +/** > =A0* spi_sync - blocking/synchronous SPI data transfers > =A0* @spi: device with which data will be exchanged > =A0* @message: describes the data transfers > diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h > index c47c4b4..c53292c 100644 > --- a/include/linux/spi/spi.h > +++ b/include/linux/spi/spi.h > @@ -214,6 +214,8 @@ static inline void spi_unregister_driver(struct spi_d= river *sdrv) > =A0* =A0 =A0 the device whose settings are being modified. > =A0* @transfer: adds a message to the controller's transfer queue. > =A0* @cleanup: frees controller-specific state > + * @lock_bus: lock SPI bus for exclusive access > + * @unlock_bus: unlock SPI bus so other devices can access > =A0* > =A0* Each SPI master controller can communicate with one or more @spi_dev= ice > =A0* children. =A0These make a small bus, sharing MOSI, MISO and SCK sign= als > @@ -286,6 +288,9 @@ struct spi_master { > > =A0 =A0 =A0 =A0/* called on release() to free memory provided by spi_mast= er */ > =A0 =A0 =A0 =A0void =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0(*cleanup)(str= uct spi_device *spi); > + > + =A0 =A0 =A0 int =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 (*lock_bus)(str= uct spi_device *spi); > + =A0 =A0 =A0 int =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 (*unlock_bus)(s= truct spi_device *spi); > =A0}; > > =A0static inline void *spi_master_get_devdata(struct spi_master *master) > @@ -578,6 +583,8 @@ spi_async(struct spi_device *spi, struct spi_message = *message) > =A0*/ > > =A0extern int spi_sync(struct spi_device *spi, struct spi_message *messag= e); > +extern int spi_lock_bus(struct spi_device *spi); > +extern int spi_unlock_bus(struct spi_device *spi); > > =A0/** > =A0* spi_write - SPI synchronous write > > > > > -- = Grant Likely, B.Sc., P.Eng. Secret Lab Technologies Ltd. ---------------------------------------------------------------------------= --- SOLARIS 10 is the OS for Data Centers - provides features such as DTrace, Predictive Self Healing and Award Winning ZFS. Get Solaris 10 NOW http://p.sf.net/sfu/solaris-dev2dev