On 4/20/23 12:27, Krzysztof Kozlowski wrote: > On 20/04/2023 18:42, Pierre-Louis Bossart wrote: >> typos in commit title... >> >> On 4/20/23 05:16, Krzysztof Kozlowski wrote: >>> The Soundwire master controllers might want to check for bus->md >> >> Apologies for being pedantic but 'manager' and 'controller' are >> different concepts in SoundWire, see DisCo spec. >> It's not a 1:1 mapping, a controller can rely on M managers > > I wrote master, not manager. For the Qualcomm case one controller is one > master, but in general I try to avoid the master/slave terminology. The Soundwire 1.2.1 spec moved away from master/slave and uses manager/peripheral. It's the same concepts, just different terms. At some point we'll update the code, it's just been too busy in 2022/2023 to do this replacement. It doesn't hurt to use the new terms. >>> initialization to avoid race between early interrupt and finish of >>> sdw_bus_master_add()/sdw_master_device_add(). Such early interrupt can >>> happen if Soundwire devices are not powered off during their probe. >>> >>> Add a store release barrier, so the Soundwire controllers can safely >>> check it in concurrent (e.g. in interrupt) way. >> >> Can you elaborate on the race condition? I am not following what breaks, >> and what entity generates the 'early interrupt'. > > The condition is explained in next patch. If you think it's better, I > can squash it with next. > > If the condition is still not clear, drop a note in next patch, so I > will elaborate there. will do. >> I am specifically concerned about adding this in common code without any >> matching smp_load_acquire() - which is only added in the following patch >> for the Qualcomm manager only, but not added for Intel/AMD managers. Is >> this not a problem? > > Shouldn't be. The barrier just won't be effective for these drivers, but > that should not be a problem, because I also did not add to these > checking bus->md in a concurrent path. > > Basically the barrier here is necessary because I want to check bus->md > in Qualcomm master interrupt handler. I really don't have any understanding or background on what this does. Is there actually a precedent for this? I mean, dealing with the device/driver model is already complicated, if now we have to be careful on when the device pointer is stored it adds a whole new element of complexity or skillset required to understand the bus operation. Re-looking at the code, the 'md' variable is allocated in sdw_master_device_add(), initialized with all kinds of values, used by device_register() so presumably when you store the value it's stored somewhere consistent, no?
