| Message ID | 1374492747-13879-2-git-send-email-Sudeep.KarkadaNagesha@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, 22 Jul 2013, Sudeep KarkadaNagesha wrote: > From: Sudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com> > > Currently different drivers requiring to access cpu device node are > parsing the device tree themselves. Since the ordering in the DT need > not match the logical cpu ordering, the parsing logic needs to consider > that. However, this has resulted in lots of code duplication and in some > cases even incorrect logic. > > It's better to consolidate them by adding support for getting cpu > device node for a given logical cpu index in DT core library. However > logical to physical index mapping can be architecture specific. > > This patch adds of_get_cpu_node to retrieve a cpu device node for a > given logical cpu index. The default matching of the physical id to the > logical cpu index can be overridden by architecture specific code. > > It is recommended to use these helper function only in pre-SMP/early > initialisation stages to retrieve CPU device node pointers in logical > ordering. Once the cpu devices are registered, it can be retrieved easily > from cpu device of_node which avoids unnecessary parsing and matching. > > Acked-by: Rob Herring <rob.herring@calxeda.com> > Signed-off-by: Sudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com> Minor nits below. Otherwise... Acked-by: Nicolas Pitre <nico@linaro.org> > --- > drivers/of/base.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ > include/linux/of.h | 6 +++++ > 2 files changed, 78 insertions(+) > > diff --git a/drivers/of/base.c b/drivers/of/base.c > index 5c54279..1e690bf 100644 > --- a/drivers/of/base.c > +++ b/drivers/of/base.c > @@ -230,6 +230,78 @@ const void *of_get_property(const struct device_node *np, const char *name, > } > EXPORT_SYMBOL(of_get_property); > > +/* > + * arch_match_cpu_phys_id - Match the given logical CPU and physical id > + * > + * @cpu: logical index of a cpu > + * @phys_id: physical identifier of a cpu > + * > + * CPU logical to physical index mapping is architecture specific. > + * However this __weak function provides a default match of physical > + * id to logical cpu index. > + * > + * Returns true if the physical identifier and the logical index correspond > + * to the same cpu, false otherwise. > + */ > +bool __weak arch_match_cpu_phys_id(int cpu, u64 phys_id) Maybe a prototype declaration for this function should be added to include/linux/of.h to avoid mismatch with architecture provided versions. > +{ > + return (u32)phys_id == cpu; > +} > + > +/** > + * of_get_cpu_node - Get device node associated with the given logical CPU > + * > + * @cpu: CPU number(logical index) for which device node is required > + * > + * The main purpose of this function is to retrieve the device node for the > + * given logical CPU index. It should be used to intialize the of_node in s/intialize/initialize/ Nicolas
Hi Nico, On 22/07/13 15:14, Nicolas Pitre wrote: > On Mon, 22 Jul 2013, Sudeep KarkadaNagesha wrote: > >> From: Sudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com> >> >> Currently different drivers requiring to access cpu device node are >> parsing the device tree themselves. Since the ordering in the DT need >> not match the logical cpu ordering, the parsing logic needs to consider >> that. However, this has resulted in lots of code duplication and in some >> cases even incorrect logic. >> >> It's better to consolidate them by adding support for getting cpu >> device node for a given logical cpu index in DT core library. However >> logical to physical index mapping can be architecture specific. >> >> This patch adds of_get_cpu_node to retrieve a cpu device node for a >> given logical cpu index. The default matching of the physical id to the >> logical cpu index can be overridden by architecture specific code. >> >> It is recommended to use these helper function only in pre-SMP/early >> initialisation stages to retrieve CPU device node pointers in logical >> ordering. Once the cpu devices are registered, it can be retrieved easily >> from cpu device of_node which avoids unnecessary parsing and matching. >> >> Acked-by: Rob Herring <rob.herring@calxeda.com> >> Signed-off-by: Sudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com> > > Minor nits below. Otherwise... > > Acked-by: Nicolas Pitre <nico@linaro.org> > Thanks for all the Acks. >> --- >> drivers/of/base.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ >> include/linux/of.h | 6 +++++ >> 2 files changed, 78 insertions(+) >> >> diff --git a/drivers/of/base.c b/drivers/of/base.c >> index 5c54279..1e690bf 100644 >> --- a/drivers/of/base.c >> +++ b/drivers/of/base.c >> @@ -230,6 +230,78 @@ const void *of_get_property(const struct device_node *np, const char *name, >> } >> EXPORT_SYMBOL(of_get_property); >> >> +/* >> + * arch_match_cpu_phys_id - Match the given logical CPU and physical id >> + * >> + * @cpu: logical index of a cpu >> + * @phys_id: physical identifier of a cpu >> + * >> + * CPU logical to physical index mapping is architecture specific. >> + * However this __weak function provides a default match of physical >> + * id to logical cpu index. >> + * >> + * Returns true if the physical identifier and the logical index correspond >> + * to the same cpu, false otherwise. >> + */ >> +bool __weak arch_match_cpu_phys_id(int cpu, u64 phys_id) > > Maybe a prototype declaration for this function should be added to > include/linux/of.h to avoid mismatch with architecture provided > versions. > Agreed, but include/linux/of.h doesn't seem to be right choice for me as this function is not really related to OF/DT. I can't choose any better place either. I don't have a strong opinion on that, just a thought. Regards, Sudeep
Hi Sudeep, I don't like this constant DT parsing every time a node of given CPU is required, but I believe it was correctly discussed with people that are more into CPU topologies and similar things than me. (My idea would be to make a lookup array with logical ID to struct device_node * mapping.) Let me just review this from DT parsing perspective. On Monday 22 of July 2013 12:32:12 Sudeep KarkadaNagesha wrote: > From: Sudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com> > > Currently different drivers requiring to access cpu device node are > parsing the device tree themselves. Since the ordering in the DT need > not match the logical cpu ordering, the parsing logic needs to consider > that. However, this has resulted in lots of code duplication and in some > cases even incorrect logic. > > It's better to consolidate them by adding support for getting cpu > device node for a given logical cpu index in DT core library. However > logical to physical index mapping can be architecture specific. > > This patch adds of_get_cpu_node to retrieve a cpu device node for a > given logical cpu index. The default matching of the physical id to the > logical cpu index can be overridden by architecture specific code. > > It is recommended to use these helper function only in pre-SMP/early > initialisation stages to retrieve CPU device node pointers in logical > ordering. Once the cpu devices are registered, it can be retrieved > easily from cpu device of_node which avoids unnecessary parsing and > matching. > > Acked-by: Rob Herring <rob.herring@calxeda.com> > Signed-off-by: Sudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com> > --- > drivers/of/base.c | 72 > ++++++++++++++++++++++++++++++++++++++++++++++++++++++ > include/linux/of.h | 6 +++++ > 2 files changed, 78 insertions(+) > > diff --git a/drivers/of/base.c b/drivers/of/base.c > index 5c54279..1e690bf 100644 > --- a/drivers/of/base.c > +++ b/drivers/of/base.c > @@ -230,6 +230,78 @@ const void *of_get_property(const struct > device_node *np, const char *name, } > EXPORT_SYMBOL(of_get_property); > > +/* > + * arch_match_cpu_phys_id - Match the given logical CPU and physical id > + * > + * @cpu: logical index of a cpu > + * @phys_id: physical identifier of a cpu > + * > + * CPU logical to physical index mapping is architecture specific. > + * However this __weak function provides a default match of physical > + * id to logical cpu index. > + * > + * Returns true if the physical identifier and the logical index > correspond + * to the same cpu, false otherwise. > + */ > +bool __weak arch_match_cpu_phys_id(int cpu, u64 phys_id) > +{ > + return (u32)phys_id == cpu; > +} > + > +/** > + * of_get_cpu_node - Get device node associated with the given logical > CPU + * > + * @cpu: CPU number(logical index) for which device node is required > + * > + * The main purpose of this function is to retrieve the device node for > the + * given logical CPU index. It should be used to intialize the > of_node in + * cpu device. Once of_node in cpu device is populated, all > the further + * references can use that instead. > + * > + * CPU logical to physical index mapping is architecture specific and > is built + * before booting secondary cores. This function uses > arch_match_cpu_phys_id + * which can be overridden by architecture > specific implementation. + * > + * Returns a node pointer for the logical cpu if found, else NULL. > + */ > +struct device_node *of_get_cpu_node(int cpu) > +{ > + struct device_node *cpun, *cpus; > + const __be32 *cell; > + u64 hwid; > + int ac, prop_len; > + > + cpus = of_find_node_by_path("/cpus"); > + if (!cpus) { > + pr_warn("Missing cpus node, bailing out\n"); > + return NULL; > + } > + > + if (of_property_read_u32(cpus, "#address-cells", &ac)) { > + pr_warn("%s: missing #address-cells\n", cpus->full_name); > + ac = of_n_addr_cells(cpus); I'm not sure this fallback is appropriate. According to ePAPR: "The #address-cells and #size-cells properties are not inherited from ancestors in the device tree. They shall be explicitly defined." In addition: If missing, a client program should assume a default value of 2 for #address-cells, and a value of 1 for #size-cells. This also leaves in question the correctness of of_n_addr_cells() and of_n_size_cells(). > + } > + > + for_each_child_of_node(cpus, cpun) { > + if (of_node_cmp(cpun->type, "cpu")) > + continue; > + cell = of_get_property(cpun, "reg", &prop_len); > + if (!cell) { > + pr_warn("%s: missing reg property\n", cpun- >full_name); > + continue; > + } > + prop_len /= sizeof(*cell); > + while (prop_len) { > + hwid = of_read_number(cell, ac); > + prop_len -= ac; > + if (arch_match_cpu_phys_id(cpu, hwid)) > + return cpun; This is a nice potential infinite loop. Consider following example: cpus { #address-cells = <2>; /* A typo. Should be 1. */ #size-cells = <0>; cpu@0 { /* ... */ reg = <0>; }; }; In this case prop_len will start with 1, while ac will be 2. After first iteration of the loop (when the phys id doesn't match) you will end up with prop_len = -1 and each iteration will decrement it even more. By the way, I'm not sure why the whole loop is here. IMHO it should be something like: if (prop_len != ac) { pr_warn(...); // or whatever continue; } hwid = of_read_number(cell, ac); // ... Best regards, Tomasz
On 15/08/13 12:32, Tomasz Figa wrote: > Hi Sudeep, > > I don't like this constant DT parsing every time a node of given CPU is > required, but I believe it was correctly discussed with people that are > more into CPU topologies and similar things than me. (My idea would be to > make a lookup array with logical ID to struct device_node * mapping.) > Yes that's the idea, see the last paragraph in the commit log. > Let me just review this from DT parsing perspective. > > On Monday 22 of July 2013 12:32:12 Sudeep KarkadaNagesha wrote: >> From: Sudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com> >> >> Currently different drivers requiring to access cpu device node are >> parsing the device tree themselves. Since the ordering in the DT need >> not match the logical cpu ordering, the parsing logic needs to consider >> that. However, this has resulted in lots of code duplication and in some >> cases even incorrect logic. >> >> It's better to consolidate them by adding support for getting cpu >> device node for a given logical cpu index in DT core library. However >> logical to physical index mapping can be architecture specific. >> >> This patch adds of_get_cpu_node to retrieve a cpu device node for a >> given logical cpu index. The default matching of the physical id to the >> logical cpu index can be overridden by architecture specific code. >> >> It is recommended to use these helper function only in pre-SMP/early >> initialisation stages to retrieve CPU device node pointers in logical >> ordering. Once the cpu devices are registered, it can be retrieved >> easily from cpu device of_node which avoids unnecessary parsing and >> matching. >> Here we go, do I need to emphasis this recommendation more ? >> Acked-by: Rob Herring <rob.herring@calxeda.com> >> Signed-off-by: Sudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com> >> --- >> drivers/of/base.c | 72 >> ++++++++++++++++++++++++++++++++++++++++++++++++++++++ >> include/linux/of.h | 6 +++++ >> 2 files changed, 78 insertions(+) >> >> diff --git a/drivers/of/base.c b/drivers/of/base.c >> index 5c54279..1e690bf 100644 >> --- a/drivers/of/base.c >> +++ b/drivers/of/base.c >> @@ -230,6 +230,78 @@ const void *of_get_property(const struct >> device_node *np, const char *name, } >> EXPORT_SYMBOL(of_get_property); >> >> +/* >> + * arch_match_cpu_phys_id - Match the given logical CPU and physical id >> + * >> + * @cpu: logical index of a cpu >> + * @phys_id: physical identifier of a cpu >> + * >> + * CPU logical to physical index mapping is architecture specific. >> + * However this __weak function provides a default match of physical >> + * id to logical cpu index. >> + * >> + * Returns true if the physical identifier and the logical index >> correspond + * to the same cpu, false otherwise. >> + */ >> +bool __weak arch_match_cpu_phys_id(int cpu, u64 phys_id) >> +{ >> + return (u32)phys_id == cpu; >> +} >> + >> +/** >> + * of_get_cpu_node - Get device node associated with the given logical >> CPU + * >> + * @cpu: CPU number(logical index) for which device node is required >> + * >> + * The main purpose of this function is to retrieve the device node for >> the + * given logical CPU index. It should be used to intialize the >> of_node in + * cpu device. Once of_node in cpu device is populated, all >> the further + * references can use that instead. >> + * >> + * CPU logical to physical index mapping is architecture specific and >> is built + * before booting secondary cores. This function uses >> arch_match_cpu_phys_id + * which can be overridden by architecture >> specific implementation. + * >> + * Returns a node pointer for the logical cpu if found, else NULL. >> + */ >> +struct device_node *of_get_cpu_node(int cpu) >> +{ >> + struct device_node *cpun, *cpus; >> + const __be32 *cell; >> + u64 hwid; >> + int ac, prop_len; >> + >> + cpus = of_find_node_by_path("/cpus"); >> + if (!cpus) { >> + pr_warn("Missing cpus node, bailing out\n"); >> + return NULL; >> + } >> + >> + if (of_property_read_u32(cpus, "#address-cells", &ac)) { >> + pr_warn("%s: missing #address-cells\n", cpus->full_name); >> + ac = of_n_addr_cells(cpus); > > I'm not sure this fallback is appropriate. According to ePAPR: > > "The #address-cells and #size-cells properties are not inherited from > ancestors in the device tree. They shall be explicitly defined." > > In addition: > > If missing, a client program should assume a default value of 2 for > #address-cells, and a value of 1 for #size-cells. > > This also leaves in question the correctness of of_n_addr_cells() and > of_n_size_cells(). > Yes agreed. We can discus that and fix it separately as it might affect multiple users. >> + } >> + >> + for_each_child_of_node(cpus, cpun) { >> + if (of_node_cmp(cpun->type, "cpu")) >> + continue; >> + cell = of_get_property(cpun, "reg", &prop_len); >> + if (!cell) { >> + pr_warn("%s: missing reg property\n", cpun- >> full_name); >> + continue; >> + } >> + prop_len /= sizeof(*cell); >> + while (prop_len) { >> + hwid = of_read_number(cell, ac); >> + prop_len -= ac; >> + if (arch_match_cpu_phys_id(cpu, hwid)) >> + return cpun; > > This is a nice potential infinite loop. Consider following example: > Good point, but based on the other discussion recently with PPC guys to support thread ids, I have changed this loop differently, it should not have this issue. Regards, Sudeep > cpus { > #address-cells = <2>; /* A typo. Should be 1. */ > #size-cells = <0>; > > cpu@0 { > /* ... */ > reg = <0>; > }; > }; > > In this case prop_len will start with 1, while ac will be 2. After first > iteration of the loop (when the phys id doesn't match) you will end up > with prop_len = -1 and each iteration will decrement it even more. > > By the way, I'm not sure why the whole loop is here. IMHO it should be > something like: > > if (prop_len != ac) { > pr_warn(...); // or whatever > continue; > } > > hwid = of_read_number(cell, ac); > // ... > > Best regards, > Tomasz >
diff --git a/drivers/of/base.c b/drivers/of/base.c index 5c54279..1e690bf 100644 --- a/drivers/of/base.c +++ b/drivers/of/base.c @@ -230,6 +230,78 @@ const void *of_get_property(const struct device_node *np, const char *name, } EXPORT_SYMBOL(of_get_property); +/* + * arch_match_cpu_phys_id - Match the given logical CPU and physical id + * + * @cpu: logical index of a cpu + * @phys_id: physical identifier of a cpu + * + * CPU logical to physical index mapping is architecture specific. + * However this __weak function provides a default match of physical + * id to logical cpu index. + * + * Returns true if the physical identifier and the logical index correspond + * to the same cpu, false otherwise. + */ +bool __weak arch_match_cpu_phys_id(int cpu, u64 phys_id) +{ + return (u32)phys_id == cpu; +} + +/** + * of_get_cpu_node - Get device node associated with the given logical CPU + * + * @cpu: CPU number(logical index) for which device node is required + * + * The main purpose of this function is to retrieve the device node for the + * given logical CPU index. It should be used to intialize the of_node in + * cpu device. Once of_node in cpu device is populated, all the further + * references can use that instead. + * + * CPU logical to physical index mapping is architecture specific and is built + * before booting secondary cores. This function uses arch_match_cpu_phys_id + * which can be overridden by architecture specific implementation. + * + * Returns a node pointer for the logical cpu if found, else NULL. + */ +struct device_node *of_get_cpu_node(int cpu) +{ + struct device_node *cpun, *cpus; + const __be32 *cell; + u64 hwid; + int ac, prop_len; + + cpus = of_find_node_by_path("/cpus"); + if (!cpus) { + pr_warn("Missing cpus node, bailing out\n"); + return NULL; + } + + if (of_property_read_u32(cpus, "#address-cells", &ac)) { + pr_warn("%s: missing #address-cells\n", cpus->full_name); + ac = of_n_addr_cells(cpus); + } + + for_each_child_of_node(cpus, cpun) { + if (of_node_cmp(cpun->type, "cpu")) + continue; + cell = of_get_property(cpun, "reg", &prop_len); + if (!cell) { + pr_warn("%s: missing reg property\n", cpun->full_name); + continue; + } + prop_len /= sizeof(*cell); + while (prop_len) { + hwid = of_read_number(cell, ac); + prop_len -= ac; + if (arch_match_cpu_phys_id(cpu, hwid)) + return cpun; + } + } + + return NULL; +} + /** Checks if the given "compat" string matches one of the strings in * the device's "compatible" property */ diff --git a/include/linux/of.h b/include/linux/of.h index 1fd08ca..9e82812 100644 --- a/include/linux/of.h +++ b/include/linux/of.h @@ -266,6 +266,7 @@ extern int of_device_is_available(const struct device_node *device); extern const void *of_get_property(const struct device_node *node, const char *name, int *lenp); +extern struct device_node *of_get_cpu_node(int cpu); #define for_each_property_of_node(dn, pp) \ for (pp = dn->properties; pp != NULL; pp = pp->next) @@ -459,6 +460,11 @@ static inline const void *of_get_property(const struct device_node *node, return NULL; } +static inline struct device_node *of_get_cpu_node(int cpu) +{ + return NULL; +} + static inline int of_property_read_u64(const struct device_node *np, const char *propname, u64 *out_value) {