Messages in this thread | | | Date | Mon, 23 Jan 2023 17:17:52 +0000 | Subject | Re: [PATCH 2/2] soundwire: bus: Allow SoundWire peripherals to register IRQ handlers | From | Richard Fitzgerald <> |
| |
On 23/01/2023 16:38, Pierre-Louis Bossart wrote: > > > On 1/23/23 10:08, Richard Fitzgerald wrote: >> On 23/01/2023 15:50, Pierre-Louis Bossart wrote: >>> >>> >>> On 1/23/23 08:53, Charles Keepax wrote: >>>> On Fri, Jan 20, 2023 at 10:20:50AM -0600, Pierre-Louis Bossart wrote: >>>>> On 1/20/23 03:59, Charles Keepax wrote: >>>>>> On Thu, Jan 19, 2023 at 11:12:04AM -0600, Pierre-Louis Bossart wrote: >>>>>>> There should be an explanation and something checking that both >>>>>>> are not >>>>>>> used concurrently. >>>>>> >>>>>> I will try to expand the explanation a litte, but I dont see any >>>>>> reason to block calling both handlers, no ill effects would come >>>>>> for a driver having both and it is useful if any soundwire >>>>>> specific steps are needed that arn't on other control buses. >>>>> >>>>> I think it's problematic if the peripheral tries to wake-up the manager >>>>> from clock-stop with both an in-band wake (i.e. drive the data line >>>>> high) and a separate GPIO-based interrupt. It's asking for trouble >>>>> IMHO. >>>>> We spent hours in the MIPI team to make sure there were no races >>>>> between >>>>> the manager-initiated restarts and peripheral-initiated restarts, >>>>> adding >>>>> a 3rd mechanism in the mix gives me a migraine already. >>>> >>>> Apologies but I am struggling see why this has any bearing on >>>> the case of a device that does both an in-band and out-of-band >>>> wake. The code we are adding in this patch will only be called in the >>>> in-band case. handle_nested_irq doesn't do any hardware magic or >>>> schedule any threads, it just calls a function that was provided >>>> when the client called request_threaded_irq. The only guarantee >>>> of atomicity you have on the interrupt_callback is sdw_dev_lock >>>> and that is being held across both calls after the patch. >>>> >>>> Could you be a little more specific on what you mean by this >>>> represents a 3rd mechanism, to me this isn't a new mechanism just >>>> an extra callback? Say for example this patch added an >>>> interrupt_callback_early to sdw_slave_ops that is called just >>>> before interrupt_callback. >>> >>> Well, the main concern is exiting the clock-stop. That is handled by the >>> manager and could be done >>> a) as the result of the framework deciding that something needs to be >>> done (typically as a result of user/applications starting a stream) >>> b) by the device with an in-band wake in case of e.g. jack detection or >>> acoustic events detected >>> c) same as b) but with a separate out-of-band interrupt. >>> >>> I'd like to make sure b) and c) are mutually-exclusive options, and that >>> the device will not throw BOTH an in-band wake and an external interrupt. >> >> Why would it be a problem if the device did (b) and (c)? >> (c) is completely invisible to the SoundWire core and not something >> that it has to handle. The handler for an out-of-band interrupt must >> call pm_runtime_get_sync() or pm_runtime_resume_and_get() and that >> would wake its own driver and the host controller. > > The Intel hardware has a power optimization for the clock-stop, which > leads to different paths to wake the system. The SoundWire IP can deal > with the data line staying high, but in the optimized mode the wakes are > signaled as DSP interrupts at a higher level. That's why we added this > intel_link_process_wakeen_event() function called from > hda_dsp_interrupt_thread(). > > So yes on paper everything would work nicely, but that's asking for > trouble with races left and right. In other words, unless you have a
Wake up from a hard INT is simply a runtime_resume of the codec driver. That is no different from ASoC runtime resuming the driver to perform some audio activity, or to access a volatile register. An event caused a runtime-resume - the driver and the host controller must resume.
The Intel code _must_ be able to safely wakeup from clock-stop if something runtime-resumes the codec driver. ASoC relies on that, and pm_runtime would be broken if that doesn't work.
> very good reason for using two wake-up mechanisms, pick a single one. > > (a) and (c) are very similar in that all the exit is handled by > pm_runtime so I am not worried too much. I do worry about paths that > were never tested and never planned for.
| |