| Message ID | 20180920161423.13990-5-wsa+renesas@sang-engineering.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | i2c: core: introduce master_xfer_irqless | expand |
On 2018-09-20 18:14, Wolfram Sang wrote: > We had the request to access devices very late when interrupts are not > available anymore multiple times now. Mostly to prepare shutdown or The first sentence is a bit backwards, I'd rephrase like so: Multiple times now we've had the request to access devices very late, when interrupts are no longer available. > reboot. Allow adapters to specify a specific callback for this case. > Note that we fall back to the generic master_xfer callback if this new > irqless one is not present. This is intentional to preserve the previous > behaviour and avoid regressions. Because there are drivers not using > interrupts or because it might have worked "accidently" before. accidentally > > Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com> > --- > drivers/i2c/i2c-core-base.c | 6 +++++- > include/linux/i2c.h | 10 +++++++--- > 2 files changed, 12 insertions(+), 4 deletions(-) > > diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c > index 904b4d2ebefa..f827446c3089 100644 > --- a/drivers/i2c/i2c-core-base.c > +++ b/drivers/i2c/i2c-core-base.c > @@ -1887,7 +1887,11 @@ int __i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num) > /* Retry automatically on arbitration loss */ > orig_jiffies = jiffies; > for (ret = 0, try = 0; try <= adap->retries; try++) { > - ret = adap->algo->master_xfer(adap, msgs, num); > + if ((in_atomic() || irqs_disabled()) && adap->algo->master_xfer_irqless) > + ret = adap->algo->master_xfer_irqless(adap, msgs, num); > + else > + ret = adap->algo->master_xfer(adap, msgs, num); > + > if (ret != -EAGAIN) > break; > if (time_after(jiffies, orig_jiffies + adap->timeout)) > diff --git a/include/linux/i2c.h b/include/linux/i2c.h > index 65b4eaed1d96..11e615123bd0 100644 > --- a/include/linux/i2c.h > +++ b/include/linux/i2c.h > @@ -498,6 +498,8 @@ i2c_register_board_info(int busnum, struct i2c_board_info const *info, > * @master_xfer: Issue a set of i2c transactions to the given I2C adapter > * defined by the msgs array, with num messages available to transfer via > * the adapter specified by adap. > + * @master_xfer_irqless: same as master_xfer. Yet, not using any interrupts "Same" (with capital 'S') to match the other entries. Also, should it not be @master_xfer to help the tools do the right thing? > + * so e.g. PMICs can be accessed very late before shutdown Trailing period. I'm fine with this change, but should it not wait until there is a user? (I think there is one in the wings, so that's a very weak objection...) Acked-by: Peter Rosin <peda@axentia.se> > * @smbus_xfer: Issue smbus transactions to the given I2C adapter. If this > * is not present, then the bus layer will try and convert the SMBus calls > * into I2C transfers instead. > @@ -511,9 +513,9 @@ i2c_register_board_info(int busnum, struct i2c_board_info const *info, > * be addressed using the same bus algorithms - i.e. bit-banging or the PCF8584 > * to name two of the most common. > * > - * The return codes from the @master_xfer field should indicate the type of > - * error code that occurred during the transfer, as documented in the kernel > - * Documentation file Documentation/i2c/fault-codes. > + * The return codes from the @master_xfer{_irqless} field should indicate the > + * type of error code that occurred during the transfer, as documented in the > + * Kernel Documentation file Documentation/i2c/fault-codes. > */ > struct i2c_algorithm { > /* If an adapter algorithm can't do I2C-level access, set master_xfer > @@ -524,6 +526,8 @@ struct i2c_algorithm { > processed, or a negative value on error */ > int (*master_xfer)(struct i2c_adapter *adap, struct i2c_msg *msgs, > int num); > + int (*master_xfer_irqless)(struct i2c_adapter *adap, > + struct i2c_msg *msgs, int num); > int (*smbus_xfer) (struct i2c_adapter *adap, u16 addr, > unsigned short flags, char read_write, > u8 command, int size, union i2c_smbus_data *data); >
On Thu, Sep 20, 2018 at 07:41:05PM +0200, Peter Rosin wrote: > On 2018-09-20 18:14, Wolfram Sang wrote: > > We had the request to access devices very late when interrupts are not > > available anymore multiple times now. Mostly to prepare shutdown or > > The first sentence is a bit backwards, I'd rephrase like so: > > Multiple times now we've had the request to access devices very late, when > interrupts are no longer available. Ok. Don't see much difference, but I don't mind. > > reboot. Allow adapters to specify a specific callback for this case. > > Note that we fall back to the generic master_xfer callback if this new > > irqless one is not present. This is intentional to preserve the previous > > behaviour and avoid regressions. Because there are drivers not using > > interrupts or because it might have worked "accidently" before. > > accidentally Thanks. > > @@ -498,6 +498,8 @@ i2c_register_board_info(int busnum, struct i2c_board_info const *info, > > * @master_xfer: Issue a set of i2c transactions to the given I2C adapter > > * defined by the msgs array, with num messages available to transfer via > > * the adapter specified by adap. > > + * @master_xfer_irqless: same as master_xfer. Yet, not using any interrupts > > "Same" (with capital 'S') to match the other entries. Also, should it > not be @master_xfer to help the tools do the right thing? I'll check. You are probably right. > > + * so e.g. PMICs can be accessed very late before shutdown > > Trailing period. > > I'm fine with this change, but should it not wait until there is a user? > (I think there is one in the wings, so that's a very weak objection...) As I mentioned in the cover-letter, this series is RFC because it is mainly meant as assistance for Stefan, so he could base his imx patches on top of it. Or the TI folks for their omap driver. I somewhen need to implement irqless transfers for the i2c-sh_mobile driver. But this may take a while, so I hope the others are first. And yes, I won't apply this series without a user and proper testing. Thanks for the review, Peter!
On Thu, Sep 20, 2018 at 06:14:23PM +0200, Wolfram Sang wrote: > We had the request to access devices very late when interrupts are not > available anymore multiple times now. Mostly to prepare shutdown or > reboot. Allow adapters to specify a specific callback for this case. > Note that we fall back to the generic master_xfer callback if this new > irqless one is not present. This is intentional to preserve the previous > behaviour and avoid regressions. Because there are drivers not using > interrupts or because it might have worked "accidently" before. It's not really about "irqless", it's about being in atomic context. irqless makes it sound like you may sleep, but the reality is sleeping is also out (the scheduler needs IRQs to do it's job.) So, it may be tempting to use things like msleep() in "irqless" but that's not permissable. So surely "atomic" would be a better name for this? Also, how does this get around the issue which I pointed out with (eg) an oops occuring, which leads to a panic followed by an attempt to reboot if the I2C bus in question is already mid-transaction? Won't we deadlock? > > Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com> > --- > drivers/i2c/i2c-core-base.c | 6 +++++- > include/linux/i2c.h | 10 +++++++--- > 2 files changed, 12 insertions(+), 4 deletions(-) > > diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c > index 904b4d2ebefa..f827446c3089 100644 > --- a/drivers/i2c/i2c-core-base.c > +++ b/drivers/i2c/i2c-core-base.c > @@ -1887,7 +1887,11 @@ int __i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num) > /* Retry automatically on arbitration loss */ > orig_jiffies = jiffies; > for (ret = 0, try = 0; try <= adap->retries; try++) { > - ret = adap->algo->master_xfer(adap, msgs, num); > + if ((in_atomic() || irqs_disabled()) && adap->algo->master_xfer_irqless) > + ret = adap->algo->master_xfer_irqless(adap, msgs, num); > + else > + ret = adap->algo->master_xfer(adap, msgs, num); > + > if (ret != -EAGAIN) > break; > if (time_after(jiffies, orig_jiffies + adap->timeout)) > diff --git a/include/linux/i2c.h b/include/linux/i2c.h > index 65b4eaed1d96..11e615123bd0 100644 > --- a/include/linux/i2c.h > +++ b/include/linux/i2c.h > @@ -498,6 +498,8 @@ i2c_register_board_info(int busnum, struct i2c_board_info const *info, > * @master_xfer: Issue a set of i2c transactions to the given I2C adapter > * defined by the msgs array, with num messages available to transfer via > * the adapter specified by adap. > + * @master_xfer_irqless: same as master_xfer. Yet, not using any interrupts > + * so e.g. PMICs can be accessed very late before shutdown > * @smbus_xfer: Issue smbus transactions to the given I2C adapter. If this > * is not present, then the bus layer will try and convert the SMBus calls > * into I2C transfers instead. > @@ -511,9 +513,9 @@ i2c_register_board_info(int busnum, struct i2c_board_info const *info, > * be addressed using the same bus algorithms - i.e. bit-banging or the PCF8584 > * to name two of the most common. > * > - * The return codes from the @master_xfer field should indicate the type of > - * error code that occurred during the transfer, as documented in the kernel > - * Documentation file Documentation/i2c/fault-codes. > + * The return codes from the @master_xfer{_irqless} field should indicate the > + * type of error code that occurred during the transfer, as documented in the > + * Kernel Documentation file Documentation/i2c/fault-codes. > */ > struct i2c_algorithm { > /* If an adapter algorithm can't do I2C-level access, set master_xfer > @@ -524,6 +526,8 @@ struct i2c_algorithm { > processed, or a negative value on error */ > int (*master_xfer)(struct i2c_adapter *adap, struct i2c_msg *msgs, > int num); > + int (*master_xfer_irqless)(struct i2c_adapter *adap, > + struct i2c_msg *msgs, int num); > int (*smbus_xfer) (struct i2c_adapter *adap, u16 addr, > unsigned short flags, char read_write, > u8 command, int size, union i2c_smbus_data *data); > -- > 2.18.0 > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
Hi Russell, I know this has been quite a while. I didn't have further time for this topic back then. But now I am going to revive and rework it. Still, thank you for your input. On Thu, Oct 18, 2018 at 11:44:46AM +0100, Russell King - ARM Linux wrote: > On Thu, Sep 20, 2018 at 06:14:23PM +0200, Wolfram Sang wrote: > > We had the request to access devices very late when interrupts are not > > available anymore multiple times now. Mostly to prepare shutdown or > > reboot. Allow adapters to specify a specific callback for this case. > > Note that we fall back to the generic master_xfer callback if this new > > irqless one is not present. This is intentional to preserve the previous > > behaviour and avoid regressions. Because there are drivers not using > > interrupts or because it might have worked "accidently" before. > > It's not really about "irqless", it's about being in atomic context. > irqless makes it sound like you may sleep, but the reality is sleeping > is also out (the scheduler needs IRQs to do it's job.) > > So, it may be tempting to use things like msleep() in "irqless" but > that's not permissable. So surely "atomic" would be a better name for > this? Full ack. It should be 'master_xfer_atomic'. > Also, how does this get around the issue which I pointed out with (eg) > an oops occuring, which leads to a panic followed by an attempt to > reboot if the I2C bus in question is already mid-transaction? Won't > we deadlock? Interesting question with multiple aspects: - The above setting will cause problems but this is orthogonal to this patch. It works by modifying __i2c_transfer() but all the locking logic is one layer above in i2c_transfer(). So, there shouldn't be a difference. - We won't deadlock, because I2C core will use trylock in this case. However, even reporting -EAGAIN won't be helpful because the interrupted transfer is likely to never finish without irqs. So, retrying won't help and we are still stuck. - Brainstorming: we could decide that if in_atomic() and master_xfer_atomic() present and the I2C client is allowed to do ATOMIC_IO (and maybe more checks), to ignore the locking and force this command on the bus. Also requiring master_xfer_atomic() to reset the IP core properly, etc. Probably also enforcing i2c_recover_bus() to ensure a free bus. This is probably the best we could do, but still no guarantees here. Some I2C devices just lock up when interrupted at the wrong time. Relying on I2C for poweroff/reboot is a somewhat fragile design to begin with. I will re-start this series with something simple, but keep the above scenario in mind. Then, we can see how much we can do, hopefully. And I got the idea for a panic-fault-injector which sounds interesting. I will try that! Kind regards, Wolfram > > > > > Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com> > > --- > > drivers/i2c/i2c-core-base.c | 6 +++++- > > include/linux/i2c.h | 10 +++++++--- > > 2 files changed, 12 insertions(+), 4 deletions(-) > > > > diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c > > index 904b4d2ebefa..f827446c3089 100644 > > --- a/drivers/i2c/i2c-core-base.c > > +++ b/drivers/i2c/i2c-core-base.c > > @@ -1887,7 +1887,11 @@ int __i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num) > > /* Retry automatically on arbitration loss */ > > orig_jiffies = jiffies; > > for (ret = 0, try = 0; try <= adap->retries; try++) { > > - ret = adap->algo->master_xfer(adap, msgs, num); > > + if ((in_atomic() || irqs_disabled()) && adap->algo->master_xfer_irqless) > > + ret = adap->algo->master_xfer_irqless(adap, msgs, num); > > + else > > + ret = adap->algo->master_xfer(adap, msgs, num); > > + > > if (ret != -EAGAIN) > > break; > > if (time_after(jiffies, orig_jiffies + adap->timeout)) > > diff --git a/include/linux/i2c.h b/include/linux/i2c.h > > index 65b4eaed1d96..11e615123bd0 100644 > > --- a/include/linux/i2c.h > > +++ b/include/linux/i2c.h > > @@ -498,6 +498,8 @@ i2c_register_board_info(int busnum, struct i2c_board_info const *info, > > * @master_xfer: Issue a set of i2c transactions to the given I2C adapter > > * defined by the msgs array, with num messages available to transfer via > > * the adapter specified by adap. > > + * @master_xfer_irqless: same as master_xfer. Yet, not using any interrupts > > + * so e.g. PMICs can be accessed very late before shutdown > > * @smbus_xfer: Issue smbus transactions to the given I2C adapter. If this > > * is not present, then the bus layer will try and convert the SMBus calls > > * into I2C transfers instead. > > @@ -511,9 +513,9 @@ i2c_register_board_info(int busnum, struct i2c_board_info const *info, > > * be addressed using the same bus algorithms - i.e. bit-banging or the PCF8584 > > * to name two of the most common. > > * > > - * The return codes from the @master_xfer field should indicate the type of > > - * error code that occurred during the transfer, as documented in the kernel > > - * Documentation file Documentation/i2c/fault-codes. > > + * The return codes from the @master_xfer{_irqless} field should indicate the > > + * type of error code that occurred during the transfer, as documented in the > > + * Kernel Documentation file Documentation/i2c/fault-codes. > > */ > > struct i2c_algorithm { > > /* If an adapter algorithm can't do I2C-level access, set master_xfer > > @@ -524,6 +526,8 @@ struct i2c_algorithm { > > processed, or a negative value on error */ > > int (*master_xfer)(struct i2c_adapter *adap, struct i2c_msg *msgs, > > int num); > > + int (*master_xfer_irqless)(struct i2c_adapter *adap, > > + struct i2c_msg *msgs, int num); > > int (*smbus_xfer) (struct i2c_adapter *adap, u16 addr, > > unsigned short flags, char read_write, > > u8 command, int size, union i2c_smbus_data *data); > > -- > > 2.18.0 > > > > > > _______________________________________________ > > linux-arm-kernel mailing list > > linux-arm-kernel@lists.infradead.org > > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel > > -- > RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ > FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up > According to speedtest.net: 11.9Mbps down 500kbps up
diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c index 904b4d2ebefa..f827446c3089 100644 --- a/drivers/i2c/i2c-core-base.c +++ b/drivers/i2c/i2c-core-base.c @@ -1887,7 +1887,11 @@ int __i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num) /* Retry automatically on arbitration loss */ orig_jiffies = jiffies; for (ret = 0, try = 0; try <= adap->retries; try++) { - ret = adap->algo->master_xfer(adap, msgs, num); + if ((in_atomic() || irqs_disabled()) && adap->algo->master_xfer_irqless) + ret = adap->algo->master_xfer_irqless(adap, msgs, num); + else + ret = adap->algo->master_xfer(adap, msgs, num); + if (ret != -EAGAIN) break; if (time_after(jiffies, orig_jiffies + adap->timeout)) diff --git a/include/linux/i2c.h b/include/linux/i2c.h index 65b4eaed1d96..11e615123bd0 100644 --- a/include/linux/i2c.h +++ b/include/linux/i2c.h @@ -498,6 +498,8 @@ i2c_register_board_info(int busnum, struct i2c_board_info const *info, * @master_xfer: Issue a set of i2c transactions to the given I2C adapter * defined by the msgs array, with num messages available to transfer via * the adapter specified by adap. + * @master_xfer_irqless: same as master_xfer. Yet, not using any interrupts + * so e.g. PMICs can be accessed very late before shutdown * @smbus_xfer: Issue smbus transactions to the given I2C adapter. If this * is not present, then the bus layer will try and convert the SMBus calls * into I2C transfers instead. @@ -511,9 +513,9 @@ i2c_register_board_info(int busnum, struct i2c_board_info const *info, * be addressed using the same bus algorithms - i.e. bit-banging or the PCF8584 * to name two of the most common. * - * The return codes from the @master_xfer field should indicate the type of - * error code that occurred during the transfer, as documented in the kernel - * Documentation file Documentation/i2c/fault-codes. + * The return codes from the @master_xfer{_irqless} field should indicate the + * type of error code that occurred during the transfer, as documented in the + * Kernel Documentation file Documentation/i2c/fault-codes. */ struct i2c_algorithm { /* If an adapter algorithm can't do I2C-level access, set master_xfer @@ -524,6 +526,8 @@ struct i2c_algorithm { processed, or a negative value on error */ int (*master_xfer)(struct i2c_adapter *adap, struct i2c_msg *msgs, int num); + int (*master_xfer_irqless)(struct i2c_adapter *adap, + struct i2c_msg *msgs, int num); int (*smbus_xfer) (struct i2c_adapter *adap, u16 addr, unsigned short flags, char read_write, u8 command, int size, union i2c_smbus_data *data);
We had the request to access devices very late when interrupts are not available anymore multiple times now. Mostly to prepare shutdown or reboot. Allow adapters to specify a specific callback for this case. Note that we fall back to the generic master_xfer callback if this new irqless one is not present. This is intentional to preserve the previous behaviour and avoid regressions. Because there are drivers not using interrupts or because it might have worked "accidently" before. Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com> --- drivers/i2c/i2c-core-base.c | 6 +++++- include/linux/i2c.h | 10 +++++++--- 2 files changed, 12 insertions(+), 4 deletions(-)