| Message ID | 20230420101617.142225-6-krzysztof.kozlowski@linaro.org (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | ASoC/soundwire: qcom: correctly probe devices after link init | expand |
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 > 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'. 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? > Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> > > --- > > Cc: Patrick Lai <quic_plai@quicinc.com> > --- > drivers/soundwire/master.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/drivers/soundwire/master.c b/drivers/soundwire/master.c > index 9b05c9e25ebe..d5bf13e7e602 100644 > --- a/drivers/soundwire/master.c > +++ b/drivers/soundwire/master.c > @@ -161,7 +161,12 @@ int sdw_master_device_add(struct sdw_bus *bus, struct device *parent, > /* add shortcuts to improve code readability/compactness */ > md->bus = bus; > bus->dev = &md->dev; > - bus->md = md; > + /* > + * Make sure the contents of md is stored before storing bus->md. > + * Paired with new slave attached and slave status interrupts > + * on the Soundwire master side. > + */ > + smp_store_release(&bus->md, md); > > pm_runtime_set_autosuspend_delay(&bus->md->dev, SDW_MASTER_SUSPEND_DELAY_MS); > pm_runtime_use_autosuspend(&bus->md->dev);
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. > >> 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. > > 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. Best regards, Krzysztof
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?
diff --git a/drivers/soundwire/master.c b/drivers/soundwire/master.c index 9b05c9e25ebe..d5bf13e7e602 100644 --- a/drivers/soundwire/master.c +++ b/drivers/soundwire/master.c @@ -161,7 +161,12 @@ int sdw_master_device_add(struct sdw_bus *bus, struct device *parent, /* add shortcuts to improve code readability/compactness */ md->bus = bus; bus->dev = &md->dev; - bus->md = md; + /* + * Make sure the contents of md is stored before storing bus->md. + * Paired with new slave attached and slave status interrupts + * on the Soundwire master side. + */ + smp_store_release(&bus->md, md); pm_runtime_set_autosuspend_delay(&bus->md->dev, SDW_MASTER_SUSPEND_DELAY_MS); pm_runtime_use_autosuspend(&bus->md->dev);
The Soundwire master controllers might want to check for bus->md 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. Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> --- Cc: Patrick Lai <quic_plai@quicinc.com> --- drivers/soundwire/master.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)