Hi, Well, unfortunately I have only a little experience with writing device drivers, so please take my comments below with a grain of salt. Also, I think it's better to discuss this on linux-pm to which some more experienced people are subscribed. On Thursday, 11 October 2007 05:13, Maxim Levitsky wrote: > Hi, > > I have few questions about .suspend()/.resume() driver functions and how best to write them. > > I have written a support for suspend/resume for saa7134 v4l driver. > Now looking at code again and again, I found few problems, and I am seeking your advice how to fix them. > > First of all the .suspend() function: > > Looking at various drivers (including v4l ones) it seems that in general the function: > > 1) tells upper layers that it is suspended > 2) saves the state of device > (generally there is nothing to save, since the driver maintains a copy of device state in memory) > > 3) disables the device (including DMA) > 4) does usual pci_save_state+pci_set_power_state(pci_dev, pci_choose_state(pci_dev, state)) > (I am talking about pci devices of course) > > But there is one problem that my .suspend() function have together with quite a lot of drivers: > It can race with IRQ handler. Suppose the handler is called just before .suspend(), and thus .suspend() literally > pulls the hadware from that handler. > > I was told that I should use synchronize_irq(), and it looks exactly like the solution. Yes, that seems to be the right solution. > But I was surprised to see that very few drivers use it in their .suspend() routines. Frankly, I'm not sure why that is so. > Another issue, even bigger happens during the resume: > Suppose the IRQ line is shared with some other device and it gets resumed first. > And my IRQ handler is called because of the other device. > Now my IRQ handler can't determine whenever the IRQ for the device, since the hardware is still powered off. > > Probably I can fix the following issues doing this: > > 1) do free_irq() in .suspend(), and request_irq() in .resume > this solves both problems since free_irq() calls synchronize_irq() > Few drivers do that this way. I would like to know if this is the right way. AFAICS, it is not and these drivers should probably be modified not to do so. The problem, as I see it, is that we don't know what state the device will be in during the resume (this may be a resume from disk and the device may have been initialized by the BIOS and we get it actually generating interrupts). > 2) Disable the card's IRQ register , then call synchronize_irq(), at that > point I can be sure that no IRQ handler is running and will run then set some > per device flag say dev->insuspend > > let IRQ handler check this flag, and bail out if set, so false interrupts are caught on resume > Probably not a good idea, since I didn't find such implementation in kernel I'm not sure of that. Sounds better than freeing the IRQs in .suspend() to me. Greetings, Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
