On Mon, 7 Jan 2013, Robert Jarzmik wrote: > Guennadi Liakhovetski <g.liakhovetski@xxxxxx> writes: > > > (adding Robert to CC) > > I don't think any data is freed by pxa_free_dma(), it only disables DMA on > > a certain channel. Theoretically there could be a different problem: > > pxa_free_dma() deactivates DMA, whereas pxa_dma_start_channels() activates > > it. But I think we're also protected against that: by the time > > pxa_camera_remove() is called, and operation on the interface has been > > stopped, client devices have been detached, pxa_camera_remove_device() has > > been called, which has also stopped the interface clock. And with clock > > stopped no interrupts can be generated. And the case of interrupt having > > been generated before clk_disabled() and only delivered to the driver so > > much later, that we're already unloading the module, seems really > > impossible to me. Robert, you agree? > > Agreed that pxa_free_dma() doesn't free anything, that one is easy :) > > And agreed too for the second part, with a slighly different explanation : > - pxa_camera_remove_device() has been called as you said > - inside this function, check comment > "/* disable capture, disable interrupts */" > => this ensures no interrupt can be generated anymore > > So after pxa_camera_remove_device() has been called, no interrupts can be > generated. > > Yet as you said, it leaves the "almost impossible" scenario : > - a user begins a capture > - the user closes the capture device and unloads pxa-camera.ko: > soc_camera_close() > pxa_camera_remove_device() > the IRQ line is asserted but doesn't trigger yet the interrupt handler > (yes I know, improbable) > meanwhile, IRQs are disabled, DMA channels are stopped > switch_to(rmmod) > => yes I know, impossible, the interrupt handler must be run before, but > let's continue for love of discussion ... > rmmod pxa-camera > pxa_camera_remove() > pxa_free_dma() * 3 > ----> here the IRQ handler kicks in !!! > => pxa_camera_irq() > pxa_dma_start_channels() > ----> it hurts ! > > My call is that this is impossible because the switch_to() should run the IRQ > handler before pxa_camera_remove() is called. > > So all this to say that I think we're safe, unless a heavy ion or a cosmic ray > strikes the PXA :) Thanks for the explanation. julia -- 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
