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

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Date:   Mon, 6 Jan 2020 14:40:19 +0530
From:   Anup Patel <anup@...infault.org>
To:     Yash Shah <yash.shah@...ive.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Bin Meng <bmeng.cn@...il.com>, green.wan@...ive.com,
        Allison Randal <allison@...utok.net>,
        Alexios Zavras <alexios.zavras@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>, bp@...e.de,
        devicetree@...r.kernel.org,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        Sachin Ghadi <sachin.ghadi@...ive.com>
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@...ive.com> 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@...ive.com>
> ---
>  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

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

>  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