RE: [PATCH v2 2/2] riscv: cacheinfo: Add support to determine no. of L2 cache way enabled

[Yash Shah]

> -----Original Message-----
> From: Anup Patel <anup@xxxxxxxxxxxxxx>
> Sent: 06 January 2020 14:40
> To: Yash Shah <yash.shah@xxxxxxxxxx>
> Cc: Rob Herring <robh+dt@xxxxxxxxxx>; Mark Rutland
> <mark.rutland@xxxxxxx>; Paul Walmsley ( Sifive)
> <paul.walmsley@xxxxxxxxxx>; Palmer Dabbelt <palmer@xxxxxxxxxxx>;
> Albert Ou <aou@xxxxxxxxxxxxxxxxx>; Bin Meng <bmeng.cn@xxxxxxxxx>;
> Green Wan <green.wan@xxxxxxxxxx>; Allison Randal <allison@xxxxxxxxxxx>;
> Alexios Zavras <alexios.zavras@xxxxxxxxx>; Greg Kroah-Hartman
> <gregkh@xxxxxxxxxxxxxxxxxxx>; Thomas Gleixner <tglx@xxxxxxxxxxxxx>;
> bp@xxxxxxx; devicetree@xxxxxxxxxxxxxxx; linux-riscv <linux-
> riscv@xxxxxxxxxxxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx List <linux-
> kernel@xxxxxxxxxxxxxxx>; Sachin Ghadi <sachin.ghadi@xxxxxxxxxx>
> Subject: Re: [PATCH v2 2/2] riscv: cacheinfo: Add support to determine no. of
> L2 cache way enabled
> 
> On Fri, Jan 3, 2020 at 9:44 AM Yash Shah <yash.shah@xxxxxxxxxx> wrote:
> >
> > In order to determine the number of L2 cache ways enabled at runtime,
> > implement a private attribute using cache_get_priv_group() in
> > cacheinfo framework. Reading this attribute
> ("number_of_ways_enabled")
> > will return the number of enabled L2 cache ways at runtime.
> >
> > Signed-off-by: Yash Shah <yash.shah@xxxxxxxxxx>
> > ---
> >  arch/riscv/include/asm/sifive_l2_cache.h |  2 ++
> >  arch/riscv/kernel/cacheinfo.c            | 31
> +++++++++++++++++++++++++++++++
> >  drivers/soc/sifive/sifive_l2_cache.c     |  5 +++++
> >  3 files changed, 38 insertions(+)
> >
> > diff --git a/arch/riscv/include/asm/sifive_l2_cache.h
> > b/arch/riscv/include/asm/sifive_l2_cache.h
> > index 04f6748..217a42f 100644
> > --- a/arch/riscv/include/asm/sifive_l2_cache.h
> > +++ b/arch/riscv/include/asm/sifive_l2_cache.h
> > @@ -10,6 +10,8 @@
> >  extern int register_sifive_l2_error_notifier(struct notifier_block
> > *nb);  extern int unregister_sifive_l2_error_notifier(struct
> > notifier_block *nb);
> >
> > +int sifive_l2_largest_wayenabled(void);
> > +
> >  #define SIFIVE_L2_ERR_TYPE_CE 0
> >  #define SIFIVE_L2_ERR_TYPE_UE 1
> >
> > diff --git a/arch/riscv/kernel/cacheinfo.c
> > b/arch/riscv/kernel/cacheinfo.c index 4c90c07..29bdb21 100644
> > --- a/arch/riscv/kernel/cacheinfo.c
> > +++ b/arch/riscv/kernel/cacheinfo.c
> > @@ -7,6 +7,7 @@
> >  #include <linux/cpu.h>
> >  #include <linux/of.h>
> >  #include <linux/of_device.h>
> > +#include <asm/sifive_l2_cache.h>
> >
> >  static void ci_leaf_init(struct cacheinfo *this_leaf,
> >                          struct device_node *node, @@ -16,6 +17,36 @@
> > static void ci_leaf_init(struct cacheinfo *this_leaf,
> >         this_leaf->type = type;
> >  }
> >
> > +#ifdef CONFIG_SIFIVE_L2
> > +static ssize_t number_of_ways_enabled_show(struct device *dev,
> > +                                          struct device_attribute *attr,
> > +                                          char *buf) {
> > +       return sprintf(buf, "%u\n", sifive_l2_largest_wayenabled()); }
> > +
> > +static DEVICE_ATTR_RO(number_of_ways_enabled);
> > +
> > +static struct attribute *priv_attrs[] = {
> > +       &dev_attr_number_of_ways_enabled.attr,
> > +       NULL,
> > +};
> > +
> > +static const struct attribute_group priv_attr_group = {
> > +       .attrs = priv_attrs,
> > +};
> > +
> > +const struct attribute_group *
> > +cache_get_priv_group(struct cacheinfo *this_leaf) {
> > +       /* We want to use private group for L2 cache only */
> > +       if (this_leaf->level == 2)
> > +               return &priv_attr_group;
> > +       else
> > +               return NULL;
> > +}
> > +#endif /* CONFIG_SIFIVE_L2 */
> > +
> 
> Instead of this, I would suggest to implement a generic ops structure.
> 
> In arch/riscv/include/asm/cacheinfo.h:
> 
> struct riscv_caceinfo_ops {
>     const struct attribute_group * (*get_priv_group)(struct cacheinfo
> *this_leaf); };
> 
> void riscv_set_cacheinfo_ops(struct riscv_caceinfo_ops *ops);
> 
> In arch/riscv/riscv/kernel/cacheinfo.h
> 
> static struct riscv_caceinfo_ops *rv_cache_ops;
> 
> void riscv_set_cacheinfo_ops(struct riscv_caceinfo_ops *ops) {
>     rv_cache_ops = ops;
> }
> EXPORT_SYMBOL_GPL(riscv_set_cacheinfo_ops);
> 
> const struct attribute_group *
> cache_get_priv_group(struct cacheinfo *this_leaf) {
>     if (rv_cache_ops && rv_cache_ops->get_priv_group)
>         return rv_cache_ops->get_priv_group(this_leaf)
>     return NULL;
> }
> 
> Above will be a separate patch. In future, we can add more ops for SOC
> specific cacheinfo.
> 
> Using riscv_set_cacheinfo_ops() you can have another patch to implement
> SiFive L2 info entirely in drivers/soc/sifive/sifive_l2_cache.c
> 

Yes I agree, the above approach is better. Will work on this approach and send new patches.

> Also, I would strongly recommend moving
> arch/riscv/include/asm/sifive_l2_cache.h
> TO
> include/soc/sifive/sifive_l2_cache.h

Sure, will send a separate patch for this.

> 
> >  static int __init_cache_level(unsigned int cpu)  {
> >         struct cpu_cacheinfo *this_cpu_ci = get_cpu_cacheinfo(cpu);
> > diff --git a/drivers/soc/sifive/sifive_l2_cache.c
> > b/drivers/soc/sifive/sifive_l2_cache.c
> > index a9ffff3..f1a5f2c 100644
> > --- a/drivers/soc/sifive/sifive_l2_cache.c
> > +++ b/drivers/soc/sifive/sifive_l2_cache.c
> > @@ -107,6 +107,11 @@ int unregister_sifive_l2_error_notifier(struct
> > notifier_block *nb)  }
> > EXPORT_SYMBOL_GPL(unregister_sifive_l2_error_notifier);
> >
> > +int sifive_l2_largest_wayenabled(void)
> > +{
> > +       return readl(l2_base + SIFIVE_L2_WAYENABLE); }
> > +
> >  static irqreturn_t l2_int_handler(int irq, void *device)  {
> >         unsigned int add_h, add_l;
> > --
> > 2.7.4
> >
> 
> Regards,
> Anup

Thanks for your comments

- Yash