Hans Verkuil <hverkuil@xxxxxxxxx> writes: > On 08/08/2016 09:30 PM, Robert Jarzmik wrote: >> The mt9m111 can be a removable module : the only case where the module >> should be kept loaded is while it is used, ie. while an active >> transation is ongoing on it. >> >> The notion of active transaction is mapped on the power state of the >> module : if powered on the removal is prohibited. > > I don't really see the purpose of this patch: if this driver is loaded > by a platform driver (such as pxa_camera), then the module count should be > 1 and it isn't possible to unload. > > So you shouldn't need this patch. Am I missing something? Well, what you are missing is ugly and twisted. With the current patchset, pxa_camera doesn't acquire the module (see pxa_camera_sensor_bound()). That is the ugly part. The reason behind is that if it acquires it, it's totally impossible to rmmod either pxa_camera or mt9m111 because of the cross-dependency I wasn't able to solve up to now. The dependency chain goes as follows : - pxa_camera should +1 refcount mt9m111 in pxa_camera_sensor_bound() - mt9m111 should +1 refcount pxa_camera through the MCLK get_clock() Without MCLK, mt9m111 is not clocked, and no I2C is available, hence no control and a total loss of context The purpose of this patch was the mt9m111 aquired a +1 refcount on pxa_camera so that pxa_camera is prevented from removal while a transfer is underway, and while the mt9m111 has the MCLK refcount acquired. I perfectly know this is suboptimal, but I didn't find a way yet to solve this. I was thinking to use pxac_fops_camera_open() to refcount +1 mt9m111 module and pxac_fops_camera_release() to refcound -1 mt9m111. But that didn't work because in order for mt9m111 to probe, the I2C has to be functional, and therefore the MCLK has to be provided. > No other driver in drivers/media/i2c does something like this. Yeah, I would bet either no other driver has the crossed dependency or they can never be rmmoded. Let me see how I can drop this patch and still prevent a kernel panic upon an rmmod of either mt9m111 or pxa_camera. Cheers. -- Robert -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
