Jiri Kosina wrote: > On Wed, 24 Feb 2010, Rick L. Vinyard, Jr. wrote: > >> The key difference is the replacement of spin_lock() with spin_trylock() >> such that if the non-interrupt code has already obtained the lock, the >> interrupt will not deadlock but instead take the else path and schedule >> a >> framebuffer update at the next interval. > > Why is _irqsave() and/or deferred work not enough? The aproach with > _trylock() seems to be overly complicated for no good reason (I personally > become very suspicious every time I see code that is using _trylock()). > I was concerned about _irqsave() because the lock is split across two functions to protect the urb after it is handed off to the usb subsystem with usb_submit_urb(). It's locked in g13_fb_send() and unlocked in the urb completion callback. As for deferred work, the g13_fb_send() is the I/O portion of the deferred framebuffer callback. I was concerned that without a lock one deferred update could hand the urb off to the usb subsystem and a second could try to access it before it was handed back to the driver. In this case the _trylock() would fail and in the else patch we would defer yet again until the next update cycle. I took this approach because usb_interrupt_msg() couldn't be used from an interrupt context, such as a resume hook because eventually down the chain it does a wait_for_completion_timeout(). It has the added benefit of reusing the urb instead of creating a new one for each framebuffer sent out, but that wasn't a reason... just a side effect. The downside is that I had to manage the urb. One thing I could do is forget about directly calling g13_fb_send() from any context and instead use the deferred framebuffer workqueue. That's probably a simpler approach anyway. > [ by the way, Rick, are you planning to resubmit the G13 driver with > incorporated feedback from the last review round? ] > Yes. I just wanted to get the details of suspend/resume worked out before resubmitting. -- Rick -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
