| Message ID | 5476071B.1060705@arm.com (mailing list archive) |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
On 26/11/14 17:00, Sudeep Holla wrote: > Hi Viresh, > [...] >> diff --git a/Documentation/devicetree/bindings/cpufreq/drivers.txt b/Documentation/devicetree/bindings/cpufreq/drivers.txt >> new file mode 100644 >> index 0000000..bd14917 >> --- /dev/null >> +++ b/Documentation/devicetree/bindings/cpufreq/drivers.txt >> @@ -0,0 +1,53 @@ >> +Binding to select which cpufreq driver to register >> + >> +It is a generic DT binding for selecting which cpufreq-driver to register for >> +any platform. >> + >> +The property listed below must be defined under node /cpus/cpu@0 node. We don't >> +support multiple CPUFreq driver currently for different cluster and so this >> +information isn't required to be present in CPUs of all clusters. >> + >> +Required properties: >> +- None >> + >> +Optional properties: >> +- dvfs-method: CPUFreq driver to probe. For example: "arm-bL-cpufreq-dt", >> + "cpufreq-dt", etc >> + > > You should manage this with compatible rather than a new property as > it's not a real hardware property. IMHO Rob's suggestion[1] should work > fine. > > IIUC, you can have the driver which create this platform device if DT > has generic compatible unconditionally(e.g "cpufreq-dt" as you have > chosen above). For all existing DT you can create a blacklist of > compatibles to match(as it doesn't have the generic compatible) covering > all the existing platforms using cpufreq-dt driver, there by you can > even remove the platform device creating from multiple places. > IMO something like the patch below should work(not tested, also > late_initcall is used just to demonstrate the idea) > > Rob, please correct me if my understanding is wrong. > > Regards, > Sudeep > > [1] > http://lists.infradead.org/pipermail/linux-arm-kernel/2014-May/256191.html > > --->8 > > diff --git a/drivers/cpufreq/cpufreq-dt.c b/drivers/cpufreq/cpufreq-dt.c > index f657c571b18e..19a616e298e0 100644 > --- a/drivers/cpufreq/cpufreq-dt.c > +++ b/drivers/cpufreq/cpufreq-dt.c > @@ -387,6 +387,32 @@ static struct platform_driver dt_cpufreq_platdrv = { > }; > module_platform_driver(dt_cpufreq_platdrv); > > +static const struct of_device_id compatible_machine_match[] = { > + /* All new machines must have the below compatible to use this > driver */ > + { .compatible = "cpufreq-generic-dt" }, > + /* BLACKLIST of existing users of cpufreq-dt below */ > + { .compatible = "samsung,exynos5420" }, > + { .compatible = "samsung,exynos5800" }, Please ignore the above 2 compatible values in this context, I just chose randomly 2 values but I now realize that there are big-little platforms and might not use this driver :( Regards, Sudeep -- To unsubscribe from this list: send the line "unsubscribe linux-pm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Hi Sudeep, On 26 November 2014 at 22:30, Sudeep Holla <sudeep.holla@arm.com> wrote: > On 26/11/14 08:46, Viresh Kumar wrote: >> We only need to have one entry in cpus@cpu0 node which will match with >> drivers >> name. > This seems fundamentally broken as the driver always needs to > unconditionally refer to cpu0. Furthermore the node need not be called > cpu0 as the name depends on its reg field. I meant CPU0's node, whatever the name is. Its normally cpu0 now a days but yes it can be something else as well :) >> We can then add another file drivers/cpufreq/device_dt.c, which will add a >> platform device with the name it finds from cpus@cpu0 node and existing >> drivers >> will work without any change. Or something else if somebody have a better >> proposal. But lets fix the bindings first. > > IIUC you will retain the existing list of cpufreq-dt platform device > creation as is. If not that breaks compatibility with old DT. I couldn't get what exactly you understood :), but this is what I meant. - Currently cpufreq drivers (like cpufreq-dt.c) are registering a platform_driver and platform specific code are registering a platform-device to match to this driver. - What will change is this platform specific code. The driver will stay as is. - Now the devices wouldn't get created from platform-specific code, but cpufreq core (may be a separate file for this: device_dt.c) will create platform device based on the string it got from DT. Makes sense? >> +Optional properties: >> +- dvfs-method: CPUFreq driver to probe. For example: "arm-bL-cpufreq-dt", >> + "cpufreq-dt", etc > > You should manage this with compatible rather than a new property as > it's not a real hardware property. IMHO Rob's suggestion[1] should work > fine. > > IIUC, you can have the driver which create this platform device if DT > has generic compatible unconditionally(e.g "cpufreq-dt" as you have > chosen above). For all existing DT you can create a blacklist of > compatibles to match(as it doesn't have the generic compatible) covering I didn't get why you asked for a blacklist here. Why wouldn't "cpufreq-dt" in compatible work for them ? > all the existing platforms using cpufreq-dt driver, there by you can > even remove the platform device creating from multiple places. Yeah, we can remove all such occurrences for a single driver this way. What I was suggesting earlier was to do this from a driver independent file, so that its done once for all possible DT drivers. Like "cpufreq-dt", "arm_big_little_dt". The same compatible property can be used there too.. > IMO something like the patch below should work(not tested, also > late_initcall is used just to demonstrate the idea) > > Rob, please correct me if my understanding is wrong. > +static const struct of_device_id compatible_machine_match[] = { > + /* All new machines must have the below compatible to use this > driver */ > + { .compatible = "cpufreq-generic-dt" }, > + /* BLACKLIST of existing users of cpufreq-dt below */ > + { .compatible = "samsung,exynos5420" }, > + { .compatible = "samsung,exynos5800" }, > + {}, > +}; > + > +static int cpufreq_generic_dt_init(void) > +{ > + struct device_node *root = of_find_node_by_path("/"); > + struct platform_device_info devinfo = { .name = "cpufreq-dt", }; > + /* > + * Initialize the device for the platforms either > + * blacklisted or compliant to generic compatible > + */ > + if (!of_match_node(compatible_machine_match, root)) > + return -ENODEV; > + > + /* Instantiate cpufreq-dt */ > + platform_device_register_full(&devinfo); > + return 0; > +} > +late_initcall(cpufreq_generic_dt_init); Looks fine to me. Looks similar to what I had in mind for creating devices from platform-independent code. -- To unsubscribe from this list: send the line "unsubscribe linux-pm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Hi, On 27/11/14 05:29, Viresh Kumar wrote: > Hi Sudeep, > > On 26 November 2014 at 22:30, Sudeep Holla <sudeep.holla@arm.com> wrote: >> On 26/11/14 08:46, Viresh Kumar wrote: >>> We only need to have one entry in cpus@cpu0 node which will match with >>> drivers >>> name. > >> This seems fundamentally broken as the driver always needs to >> unconditionally refer to cpu0. Furthermore the node need not be called >> cpu0 as the name depends on its reg field. > > I meant CPU0's node, whatever the name is. Its normally cpu0 now a days > but yes it can be something else as well :) > Not really ;), have a look @ arch/arm/boot/dts/highbank.dts >>> We can then add another file drivers/cpufreq/device_dt.c, which will add a >>> platform device with the name it finds from cpus@cpu0 node and existing >>> drivers >>> will work without any change. Or something else if somebody have a better >>> proposal. But lets fix the bindings first. >> >> IIUC you will retain the existing list of cpufreq-dt platform device >> creation as is. If not that breaks compatibility with old DT. > > I couldn't get what exactly you understood :), but this is what I meant. > - Currently cpufreq drivers (like cpufreq-dt.c) are registering a > platform_driver > and platform specific code are registering a platform-device to match to this > driver. > - What will change is this platform specific code. The driver will stay as is. > - Now the devices wouldn't get created from platform-specific code, but > cpufreq core (may be a separate file for this: device_dt.c) will create platform > device based on the string it got from DT. > > Makes sense? > No that won't suffice. You can't modify the DTs of the platforms using cpufreq-dt.c as of today. They should continue to work, so either you retain all the existing platform device creation in platform code as is or do something like below with the blacklist for those platforms. > >>> +Optional properties: >>> +- dvfs-method: CPUFreq driver to probe. For example: "arm-bL-cpufreq-dt", >>> + "cpufreq-dt", etc >> >> You should manage this with compatible rather than a new property as >> it's not a real hardware property. IMHO Rob's suggestion[1] should work >> fine. >> >> IIUC, you can have the driver which create this platform device if DT >> has generic compatible unconditionally(e.g "cpufreq-dt" as you have >> chosen above). For all existing DT you can create a blacklist of >> compatibles to match(as it doesn't have the generic compatible) covering > > I didn't get why you asked for a blacklist here. Why wouldn't "cpufreq-dt" in > compatible work for them ? > Again for backward compatibility reasons :) >> all the existing platforms using cpufreq-dt driver, there by you can >> even remove the platform device creating from multiple places. > > Yeah, we can remove all such occurrences for a single driver this way. > What I was suggesting earlier was to do this from a driver independent > file, so that its done once for all possible DT drivers. Like "cpufreq-dt", > "arm_big_little_dt". The same compatible property can be used there > too.. > >> IMO something like the patch below should work(not tested, also >> late_initcall is used just to demonstrate the idea) >> >> Rob, please correct me if my understanding is wrong. > >> +static const struct of_device_id compatible_machine_match[] = { >> + /* All new machines must have the below compatible to use this >> driver */ >> + { .compatible = "cpufreq-generic-dt" }, >> + /* BLACKLIST of existing users of cpufreq-dt below */ >> + { .compatible = "samsung,exynos5420" }, >> + { .compatible = "samsung,exynos5800" }, >> + {}, >> +}; >> + >> +static int cpufreq_generic_dt_init(void) >> +{ >> + struct device_node *root = of_find_node_by_path("/"); >> + struct platform_device_info devinfo = { .name = "cpufreq-dt", }; >> + /* >> + * Initialize the device for the platforms either >> + * blacklisted or compliant to generic compatible >> + */ >> + if (!of_match_node(compatible_machine_match, root)) >> + return -ENODEV; >> + >> + /* Instantiate cpufreq-dt */ >> + platform_device_register_full(&devinfo); >> + return 0; >> +} >> +late_initcall(cpufreq_generic_dt_init); > > Looks fine to me. Looks similar to what I had in mind for creating > devices from platform-independent code. > OK, in this way you still continue to work on existing platforms with *old DT*. Regards, Sudeep -- To unsubscribe from this list: send the line "unsubscribe linux-pm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 27 November 2014 at 15:24, Sudeep Holla <sudeep.holla@arm.com> wrote: > No that won't suffice. You can't modify the DTs of the platforms using > cpufreq-dt.c as of today. They should continue to work, so either you > retain all the existing platform device creation in platform code as is > or do something like below with the blacklist for those platforms. Is the meaning of "backward compatibility" for DTs mentioned somewhere? I am not sure if we have to *always* follow the compatibility you are talking about. Probably we want new DTs to continue supporting older version of kernels. Not that older DTs should work with new kernel changes. So, even with another field in cpuX node, we wouldn't break older kernels as they will anyway get the device from platform code. @Rob? > OK, in this way you still continue to work on existing platforms with > *old DT*. Probably not. -- To unsubscribe from this list: send the line "unsubscribe linux-pm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 27/11/14 10:22, Viresh Kumar wrote: > On 27 November 2014 at 15:24, Sudeep Holla <sudeep.holla@arm.com> wrote: >> No that won't suffice. You can't modify the DTs of the platforms using >> cpufreq-dt.c as of today. They should continue to work, so either you >> retain all the existing platform device creation in platform code as is >> or do something like below with the blacklist for those platforms. > > Is the meaning of "backward compatibility" for DTs mentioned somewhere? > I am not sure if we have to *always* follow the compatibility you are talking > about. > It's the general understanding, I am not sure if it's specified anywhere in the kernel Documentation, but I could find the below excerpts from [1]: "The compatibility rules say that new kernels must work with older device trees. If changes are required, they should be put into new properties; the old ones can then be deprecated but not removed. New properties should be optional, so that device trees lacking those properties continue to work. The device tree developers will provide a set of guidelines for the creation of future-proof bindings." > Probably we want new DTs to continue supporting older version of kernels. > Not that older DTs should work with new kernel changes. > It's *exactly opposite* as DTs are considered as part of firmware that gets shipped with the boards and any kernel should work with that DT if it is compliance with the DT bindings(even old, as the DT bindings should never get changed only gets extended) > So, even with another field in cpuX node, we wouldn't break older kernels > as they will anyway get the device from platform code. > Yes, but that's not what we want. >> OK, in this way you still continue to work on existing platforms with >> *old DT*. > > Probably not. > No, you *must* :). That's backward compatibility. Just consider a simple case where the bootloader is generating DT and we don't want to upgrade it. Regards, Sudeep [1] http://lwn.net/Articles/572114/ -- To unsubscribe from this list: send the line "unsubscribe linux-pm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 27 November 2014 at 16:45, Sudeep Holla <sudeep.holla@arm.com> wrote: > It's the general understanding, I am not sure if it's specified anywhere > in the kernel Documentation, but I could find the below excerpts from [1]: > > "The compatibility rules say that new kernels must work with older > device trees. If changes are required, they should be put into new > properties; the old ones can then be deprecated but not removed. New > properties should be optional, so that device trees lacking those > properties continue to work. The device tree developers will provide a > set of guidelines for the creation of future-proof bindings." > > It's *exactly opposite* as DTs are considered as part of firmware that > gets shipped with the boards and any kernel should work with that DT if > it is compliance with the DT bindings(even old, as the DT bindings > should never get changed only gets extended) Okay, I was completely wrong. :) > No, you *must* :). That's backward compatibility. Just consider a simple > case where the bootloader is generating DT and we don't want to upgrade it. Now these are the options we have for existing platforms: - Update those platforms to check if DT has "compatible" string in CPU node. If yes, don't create a device as this will be created by cpufreq-dt. - Just remove the device creation from those paths if the Maintainers of those platforms want to cleanup their code, accepting the loss of backward compatibility.. -- viresh -- To unsubscribe from this list: send the line "unsubscribe linux-pm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 28/11/14 06:31, Viresh Kumar wrote: > On 27 November 2014 at 16:45, Sudeep Holla <sudeep.holla@arm.com> wrote: >> It's the general understanding, I am not sure if it's specified anywhere >> in the kernel Documentation, but I could find the below excerpts from [1]: >> >> "The compatibility rules say that new kernels must work with older >> device trees. If changes are required, they should be put into new >> properties; the old ones can then be deprecated but not removed. New >> properties should be optional, so that device trees lacking those >> properties continue to work. The device tree developers will provide a >> set of guidelines for the creation of future-proof bindings." >> >> It's *exactly opposite* as DTs are considered as part of firmware that >> gets shipped with the boards and any kernel should work with that DT if >> it is compliance with the DT bindings(even old, as the DT bindings >> should never get changed only gets extended) > > Okay, I was completely wrong. :) > >> No, you *must* :). That's backward compatibility. Just consider a simple >> case where the bootloader is generating DT and we don't want to upgrade it. > > Now these are the options we have for existing platforms: > > - Update those platforms to check if DT has "compatible" string in CPU node. > If yes, don't create a device as this will be created by cpufreq-dt. > This fixes how it will work with new DTs, how about old DTs ? IMO we still need the blacklist kind of logic I sent before. Do you see any issues with that ? > - Just remove the device creation from those paths if the Maintainers of > those platforms want to cleanup their code, accepting the loss of backward > compatibility.. > I don't think this is something acceptable, why will someone want to lose a working feature with new kernel. Regards, Sudeep -- To unsubscribe from this list: send the line "unsubscribe linux-pm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 28 November 2014 at 17:21, Sudeep Holla <sudeep.holla@arm.com> wrote: >> - Update those platforms to check if DT has "compatible" string in CPU >> node. >> If yes, don't create a device as this will be created by cpufreq-dt. >> > > This fixes how it will work with new DTs, how about old DTs ? > IMO we still need the blacklist kind of logic I sent before. Yes.. > I don't think this is something acceptable, why will someone want to > lose a working feature with new kernel. If some platform maintainers care for cleaner/simpler code instead of backward compatibility .. For example, exynos has just started to use cpufreq-dt. Probably in 3.18 or may be 19 as well.. So, they might not care about backward compatibility at all.. Let me see if I can come up with a solution that looks reasonably clean. -- viresh -- To unsubscribe from this list: send the line "unsubscribe linux-pm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/cpufreq/cpufreq-dt.c b/drivers/cpufreq/cpufreq-dt.c index f657c571b18e..19a616e298e0 100644 --- a/drivers/cpufreq/cpufreq-dt.c +++ b/drivers/cpufreq/cpufreq-dt.c @@ -387,6 +387,32 @@ static struct platform_driver dt_cpufreq_platdrv = { }; module_platform_driver(dt_cpufreq_platdrv); +static const struct of_device_id compatible_machine_match[] = { + /* All new machines must have the below compatible to use this driver */ + { .compatible = "cpufreq-generic-dt" }, + /* BLACKLIST of existing users of cpufreq-dt below */ + { .compatible = "samsung,exynos5420" }, + { .compatible = "samsung,exynos5800" }, + {}, +}; + +static int cpufreq_generic_dt_init(void) +{ + struct device_node *root = of_find_node_by_path("/"); + struct platform_device_info devinfo = { .name = "cpufreq-dt", }; + /* + * Initialize the device for the platforms either + * blacklisted or compliant to generic compatible + */ + if (!of_match_node(compatible_machine_match, root)) + return -ENODEV; + + /* Instantiate cpufreq-dt */ + platform_device_register_full(&devinfo); + return 0; +} +late_initcall(cpufreq_generic_dt_init); + -- To unsubscribe from this list: send the line "unsubscribe linux-pm" in