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Date:   Thu, 17 Feb 2022 11:44:04 +0530
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Subject: Re: [PATCH v5 1/2] remoteproc: Introduce sysfs_read_only flag
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To:     Bjorn Andersson <bjorn.andersson@linaro.org>
CC:     <kishon@ti.com>, <vigneshr@ti.com>, <s-anna@ti.com>,
        <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> <Yg1Y1dtT9CjZTxgW@yoga>
From:   Puranjay Mohan <p-mohan@ti.com>
In-Reply-To: <Yg1Y1dtT9CjZTxgW@yoga>
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Hi Bjorn,

On 17/02/22 01:34, Bjorn Andersson wrote:
> On Wed 16 Feb 02:12 CST 2022, 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;
> 
> Change looks good now, but just to make sure, you actually care about
> the content of these files for the Wakup M3? Read-only vs hiding them...

Yes, it is useful for debugging purposes, hence making it read-only is
the correct approach.

Also, I will be re-sending PRU remoteproc consumer API patch series[1]
that depends on this change.

[1]https://patchwork.kernel.org/project/linux-remoteproc/cover/20201216165239.2744-1-grzegorz.jaszczyk@linaro.org/

Thanks,
Puranjay Mohan

> 
> regards,
> Bjorn
> 
>> +
>> +	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;
>> -- 
>> 2.17.1
>>