Hi David, On Tue, Sep 23, 2014 at 12:58:54PM -0700, David E. Box wrote: > Hi Maxime, > > On Tue, Sep 23, 2014 at 09:00:57PM +0200, Maxime Ripard wrote: > > Hi David, > > > > On Tue, Sep 23, 2014 at 11:40:26AM -0700, David E. Box wrote: > > > This patch implements an I2C bus sharing mechanism between the host and > > > platform > > > hardware on select Intel BayTrail SoC platforms using the X-Powers AXP288 > > > PMIC. > > > > > > On these platforms access to the PMIC must be shared with platform > > > hardware. The > > > hardware unit assumes full control of the I2C bus and the host must > > > request > > > access through a special semaphore. Hardware control of the bus also > > > makes it > > > necessary to disable runtime pm to avoid interfering with hardware > > > transactions. > > > > > > Signed-off-by: David E. Box <david.e....@linux.intel.com> > > > > Sorry for stepping in like this without really knowing your platform, > > but wouldn't using the hwspinlock framework make more sense than > > hardcoding your own internal functions here? > > I looked into this but didn't see a clear way on our platform to identify the > semaphore seperately from doing it in the designware platform driver. The way > we can find it now is through evaluating an ACPI _SEM object on every i2c > device > that gets probed by the dw driver since at probe time we can get the acpi > handle.
And you have no way to turn it around and identify which semaphore is associated to which i2c bus? If so, there is probably some way to associate a given instance of the i2c driver to one semaphore. > Without this handle however there isn't a clear way of evaluating the _SEM > object which would be needed to register a hwspinlock in separate code. > > Plus it would still require changes to the designware i2c core, though > admittedly > having a generic hwspinlock pointer added to the struct is cleaner. Not only cleaner, but that could also be used by other platforms that are using this I2C driver (and since it's a designware IP, there must be quite a lot) together with hardware locking. Maxime -- Maxime Ripard, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com
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