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Subject: Re: [PATCH v5 1/2] remoteproc: Introduce sysfs_read_only flag
To:     Puranjay Mohan <p-mohan@ti.com>, <vigneshr@ti.com>,
        <s-anna@ti.com>, <bjorn.andersson@linaro.org>,
        <mathieu.poirier@linaro.org>, <linux-remoteproc@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>
References: <20220216081224.9956-1-p-mohan@ti.com>
 <20220216081224.9956-2-p-mohan@ti.com>
From:   Kishon Vijay Abraham I <kishon@ti.com>
Message-ID: <0d44d73f-d882-83db-9cf2-09f7cdc91ab2@ti.com>
Date:   Fri, 18 Feb 2022 10:30:37 +0530
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On 16/02/22 1:42 pm, Puranjay Mohan wrote:
> The remoteproc framework provides sysfs interfaces for changing
> the firmware name and for starting/stopping a remote processor
> through the sysfs files 'state' and 'firmware'. The 'coredump'
> file is used to set the coredump configuration. The 'recovery'
> sysfs file can also be used similarly to control the error recovery
> state machine of a remoteproc. These interfaces are currently
> allowed irrespective of how the remoteprocs were booted (like
> remoteproc self auto-boot, remoteproc client-driven boot etc).
> These interfaces can adversely affect a remoteproc and its clients
> especially when a remoteproc is being controlled by a remoteproc
> client driver(s). Also, not all remoteproc drivers may want to
> support the sysfs interfaces by default.
> 
> Add support to make the remoteproc sysfs files read only by
> introducing a state flag 'sysfs_read_only' that the individual
> remoteproc drivers can set based on their usage needs. The default
> behavior is to allow the sysfs operations as before.
> 
> Implement attribute_group->is_visible() to make the sysfs
> entries read only when 'sysfs_read_only' flag is set.
> 
> Signed-off-by: Puranjay Mohan <p-mohan@ti.com>
> Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
> ---
> Changes in v4->v5:
> Rename deny_sysfs_ops to sysfs_read_only.
> Make coredump readonly with other files.
> 
> Changes in v3->v4:
> Use mode = 0444 in rproc_is_visible() to make the sysfs entries
> read-only when the deny_sysfs_ops flag is set.
> ---
>  drivers/remoteproc/remoteproc_sysfs.c | 19 ++++++++++++++++++-
>  include/linux/remoteproc.h            |  2 ++
>  2 files changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/remoteproc/remoteproc_sysfs.c b/drivers/remoteproc/remoteproc_sysfs.c
> index ea8b89f97d7b..abf0cd05d5e1 100644
> --- a/drivers/remoteproc/remoteproc_sysfs.c
> +++ b/drivers/remoteproc/remoteproc_sysfs.c
> @@ -230,6 +230,22 @@ static ssize_t name_show(struct device *dev, struct device_attribute *attr,
>  }
>  static DEVICE_ATTR_RO(name);
>  
> +static umode_t rproc_is_visible(struct kobject *kobj, struct attribute *attr,
> +				int n)
> +{
> +	struct device *dev = kobj_to_dev(kobj);
> +	struct rproc *rproc = to_rproc(dev);
> +	umode_t mode = attr->mode;
> +
> +	if (rproc->sysfs_read_only && (attr == &dev_attr_recovery.attr ||
> +				       attr == &dev_attr_firmware.attr ||
> +				       attr == &dev_attr_state.attr ||
> +				       attr == &dev_attr_coredump.attr))
> +		mode = 0444;

Nitpick: use S_IRUGO instead of 0444.

Thanks,
Kishon
> +
> +	return mode;
> +}
> +
>  static struct attribute *rproc_attrs[] = {
>  	&dev_attr_coredump.attr,
>  	&dev_attr_recovery.attr,
> @@ -240,7 +256,8 @@ static struct attribute *rproc_attrs[] = {
>  };
>  
>  static const struct attribute_group rproc_devgroup = {
> -	.attrs = rproc_attrs
> +	.attrs = rproc_attrs,
> +	.is_visible = rproc_is_visible,
>  };
>  
>  static const struct attribute_group *rproc_devgroups[] = {
> diff --git a/include/linux/remoteproc.h b/include/linux/remoteproc.h
> index e0600e1e5c17..93a1d0050fbc 100644
> --- a/include/linux/remoteproc.h
> +++ b/include/linux/remoteproc.h
> @@ -523,6 +523,7 @@ struct rproc_dump_segment {
>   * @table_sz: size of @cached_table
>   * @has_iommu: flag to indicate if remote processor is behind an MMU
>   * @auto_boot: flag to indicate if remote processor should be auto-started
> + * @sysfs_read_only: flag to make remoteproc sysfs files read only
>   * @dump_segments: list of segments in the firmware
>   * @nb_vdev: number of vdev currently handled by rproc
>   * @elf_class: firmware ELF class
> @@ -562,6 +563,7 @@ struct rproc {
>  	size_t table_sz;
>  	bool has_iommu;
>  	bool auto_boot;
> +	bool sysfs_read_only;
>  	struct list_head dump_segments;
>  	int nb_vdev;
>  	u8 elf_class;
>