Re: [PATCH v2 3/4] rpmsg: char: Add possibility to use default endpoint of the rpmsg device.

Arnaud POULIQUEN
2021-07-01T07:34:27Z

Hello Mathieu,

On 6/30/21 10:48 PM, Mathieu Poirier wrote:
> On Wed, Jun 23, 2021 at 05:05:03PM +0200, Arnaud Pouliquen wrote:
>> Current implementation create/destroy a new endpoint on each
>> rpmsg_eptdev_open/rpmsg_eptdev_release calls.
>>
>> For a rpmsg device created by the NS announcement mechanism we need to
>> use a unique static endpoint that is the default rpmsg device endpoint
>> associated to the channel.
>>
>> This patch prepares the introduction of a rpmsg channel device for the
>> char device. The rpmsg channel device will require a default endpoint to
>> communicate to the remote processor.
>>
>> Add the static_ept field in rpmsg_eptdev structure. This boolean
>> determines the behavior on rpmsg_eptdev_open and rpmsg_eptdev_release call.
>>
>> - If static_ept == false:
>> Use the legacy behavior by creating a new endpoint each time
>> rpmsg_eptdev_open is called and release it when rpmsg_eptdev_release
>> is called on /dev/rpmsgX device open/close.
>>
>> - If static_ept == true:
>> use the rpmsg device default endpoint for the communication.
>> - Address the update of _rpmsg_chrdev_eptdev_create in e separate patch for readability.
>>
>> Add protection in rpmsg_eptdev_ioctl to prevent to destroy a default endpoint.
>>
>> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
>> ---
>> update vs V1:
>> - remove the management of the default endpoint creation from rpmsg_eptdev_open.
>>
>> ---
>> drivers/rpmsg/rpmsg_char.c | 21 +++++++++++++++++++--
>> 1 file changed, 19 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
>> index 50b7d4b00175..a75dce1e29d8 100644
>> --- a/drivers/rpmsg/rpmsg_char.c
>> +++ b/drivers/rpmsg/rpmsg_char.c
>> @@ -45,6 +45,8 @@ static DEFINE_IDA(rpmsg_minor_ida);
>> * @queue_lock: synchronization of @queue operations
>> * @queue: incoming message queue
>> * @readq: wait object for incoming queue
>> + * @static_ept: specify if the endpoint has to be created at each device opening or
>> + * if the default endpoint should be used.
>> */
>> struct rpmsg_eptdev {
>> struct device dev;
>> @@ -59,6 +61,8 @@ struct rpmsg_eptdev {
>> spinlock_t queue_lock;
>> struct sk_buff_head queue;
>> wait_queue_head_t readq;
>> +
>> + bool static_ept;
>> };
>>
>> int rpmsg_chrdev_eptdev_destroy(struct device *dev, void *data)
>> @@ -116,7 +120,15 @@ static int rpmsg_eptdev_open(struct inode *inode, struct file *filp)
>>
>> get_device(dev);
>>
>> - ept = rpmsg_create_ept(rpdev, rpmsg_ept_cb, eptdev, eptdev->chinfo);
>> + /*
>> + * If the static_ept is set to true, the rpmsg device default endpoint is used.
>> + * Else a new endpoint is created on open that will be destroyed on release.
>> + */
>> + if (eptdev->static_ept)
>> + ept = rpdev->ept;
>> + else
>> + ept = rpmsg_create_ept(rpdev, rpmsg_ept_cb, eptdev, eptdev->chinfo);
>> +
>> if (!ept) {
>> dev_err(dev, "failed to open %s\n", eptdev->chinfo.name);
>> put_device(dev);
>> @@ -137,7 +149,8 @@ static int rpmsg_eptdev_release(struct inode *inode, struct file *filp)
>> /* Close the endpoint, if it's not already destroyed by the parent */
>> mutex_lock(&eptdev->ept_lock);
>> if (eptdev->ept) {
>> - rpmsg_destroy_ept(eptdev->ept);
>> + if (!eptdev->static_ept)
>> + rpmsg_destroy_ept(eptdev->ept);
>> eptdev->ept = NULL;
>> }
>> mutex_unlock(&eptdev->ept_lock);
>> @@ -264,6 +277,10 @@ static long rpmsg_eptdev_ioctl(struct file *fp, unsigned int cmd,
>> if (cmd != RPMSG_DESTROY_EPT_IOCTL)
>> return -EINVAL;
>>
>> + /* Don't allow to destroy a default endpoint. */
>> + if (!eptdev->rpdev || eptdev->ept == eptdev->rpdev->ept)
>
> Did you find a scenario where eptdev->rpdev would not be valid when this is
> called? To me if this code is called __rpmsg_chrdev_eptdev_create() has setup
> the rpdev pointer and therefore it will be valid.
>
> If there is a scenario where it is possible that eptdev->rpdev is invalid then
> please add a comment with the details. Otherwise simply remove the first part
> of the condition.
>
> Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>

Good catch!
you are right, it seems an over protection, i will verify this making a new
revision that will take into account your other remarks.

Thanks for all your advices and patchset reviews related to rpmsg_char
restructuring.

Arnaud

>
>> + return -EPERM;
>> +
>> return rpmsg_chrdev_eptdev_destroy(&eptdev->dev, NULL);
>> }
>>
>> --
>> 2.17.1
>>