linux-kernel - Re: [PATCH RESEND] rpmsg: Add driver_override device attribute for rpmsg

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Date:   Wed, 21 Mar 2018 13:29:58 +0530
From:   Anup Patel <anup@...infault.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Ohad Ben-Cohen <ohad@...ery.com>, linux-remoteproc@...r.kernel.org,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RESEND] rpmsg: Add driver_override device attribute for rpmsg_device

On Mon, Mar 19, 2018 at 4:17 AM, Bjorn Andersson
<bjorn.andersson@...aro.org> wrote:
> On Wed 10 Jan 05:17 PST 2018, Anup Patel wrote:
>
>> This patch adds "driver_override" device attribute for rpmsg_device which
>> will allow users to explicitly specify the rpmsg_driver to be used via
>> sysfs entry.
>>
>> The "driver_override" device attribute implemented here is very similar
>> to "driver_override" implemented for platform, pci, and amba bus types.
>>
>> One important use-case of "driver_override" device attribute is to force
>> use of rpmsg_chrdev driver for certain rpmsg_device instances.
>>
>
> I assume you mean specifically for the case where you want to prevent
> some kernel driver to probe for some given channel?

Yes, there are few use-cases where we want to prevent kernel
driver and rather access rpmsg device from user-space using
rpmsg_chrdev driver.

>
> The intention with rpmsg_char is that you through the rpmsg_ctrlX
> interface create and destroy endpoints dynamically, so you wouldn't need
> to use this mechanism to bind some specific channel to rpmsg_char.
>
>
> That said, this does make sense for completeness sake.
>
> [..]
>> diff --git a/drivers/rpmsg/rpmsg_core.c b/drivers/rpmsg/rpmsg_core.c
>> index dffa3aa..9a25e42 100644
>> --- a/drivers/rpmsg/rpmsg_core.c
>> +++ b/drivers/rpmsg/rpmsg_core.c
>> @@ -321,11 +321,11 @@ struct device *rpmsg_find_device(struct device *parent,
>>  }
>>  EXPORT_SYMBOL(rpmsg_find_device);
>>
>> -/* sysfs show configuration fields */
>> +/* sysfs configuration fields */
>>  #define rpmsg_show_attr(field, path, format_string)                  \
>>  static ssize_t                                                               \
>>  field##_show(struct device *dev,                                     \
>> -                     struct device_attribute *attr, char *buf)       \
>> +          struct device_attribute *attr, char *buf)                  \
>
> Seems unnecessary.

OK, I will drop these changes.

>
>>  {                                                                    \
>>       struct rpmsg_device *rpdev = to_rpmsg_device(dev);              \
>>                                                                       \
>> @@ -333,11 +333,52 @@ field##_show(struct device *dev,                                        \
>>  }                                                                    \
>>  static DEVICE_ATTR_RO(field);
>>
>> +#define rpmsg_string_attr(field, path)                                       \
>
> "path" is an odd name for these, I think it's a "member".
>
>> +static ssize_t                                                               \
>> +field##_store(struct device *dev,                                    \
>> +           struct device_attribute *attr, const char *buf, size_t sz)\
>
> field##_store(struct device *dev, struct device_attribute *attr,        \
>               const char *buf, size_t sz)                               \
>
> Is prettier

OK, I will update this.

>
>> +{                                                                    \
>> +     struct rpmsg_device *rpdev = to_rpmsg_device(dev);              \
>> +     char *new, *old, *cp;                                           \
>> +                                                                     \
>> +     new = kstrndup(buf, sz, GFP_KERNEL);                            \
>> +     if (!new)                                                       \
>> +             return -ENOMEM;                                         \
>> +                                                                     \
>> +     cp = strchr(new, '\n');                                         \
>> +     if (cp)                                                         \
>> +             *cp = '\0';                                             \
>
> I prefer
>
>         new[strcspn(new, "\n")] = '\0';

Sure, I will update this.

Thanks,
Anup