Re: [PATCH 3/4] rpmsg: char: Introduce the "rpmsg-raw" channel

Arnaud POULIQUEN
2021-06-16T12:38:39Z

Hi Mathieu,

On 6/15/21 10:01 PM, Mathieu Poirier wrote:
> On Mon, Jun 07, 2021 at 07:30:31PM +0200, Arnaud Pouliquen wrote:
>> Allows to probe the endpoint device on a remote name service announcement,
>> by registering a rpmsg_driverfor the "rpmsg-raw" channel.
>>
>> With this patch the /dev/rpmsgX interface can be instantiated by the remote
>> firmware.
>>
>> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
>> ---
>> drivers/rpmsg/rpmsg_char.c | 54 ++++++++++++++++++++++++++++++++++++--
>> 1 file changed, 52 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
>> index 4199ac1bee10..3b850b218eb0 100644
>> --- a/drivers/rpmsg/rpmsg_char.c
>> +++ b/drivers/rpmsg/rpmsg_char.c
>> @@ -25,6 +25,8 @@
>>
>> #include "rpmsg_char.h"
>>
>> +#define RPMSG_CHAR_DEVNAME "rpmsg-raw"
>> +
>> static dev_t rpmsg_major;
>> static struct class *rpmsg_class;
>>
>> @@ -416,6 +418,40 @@ int rpmsg_chrdev_eptdev_create(struct rpmsg_device *rpdev, struct device *parent
>> }
>> EXPORT_SYMBOL(rpmsg_chrdev_eptdev_create);
>>
>> +static int rpmsg_chrdev_probe(struct rpmsg_device *rpdev)
>> +{
>> + struct rpmsg_channel_info chinfo;
>> +
>> + memcpy(chinfo.name, RPMSG_CHAR_DEVNAME, sizeof(RPMSG_CHAR_DEVNAME));
>> + chinfo.src = rpdev->src;
>> + chinfo.dst = rpdev->dst;
>> +
>> + return __rpmsg_chrdev_eptdev_create(rpdev, &rpdev->dev, chinfo, true);
>
> I am a little puzzled here as to why we need different modes... Why can't we
> simply call rpmsg_chrdev_eptdev_create() and let the endpoint be created on
> open() and destroyed on release() as per the current implementation?

The main reason is the support of the NS announcement
a NS announcement is received from the remote processor:
channel name: "rpmsg-raw"
remote address (dst address): 0x400
local address (scr address) : RPMSG_ADDR_ANY
=> no default endpoint, and not local address.

case 1) if we use legacy implementation ( no default endpoint)
=> create/destroy endpoint on open/stop
- on first open: created endpoint is bound to scr address 0x406
- a first message is sent to the remote side, the address 0x406 is stored as
default channel dst address on remote side.
- on close: endpoint is closed and associated address 0x406 is free.
- another driver create an enpoint the address 0x406 is reserved for this new
endpoint.
- on new open: scr address is set to next value 0x407
=> how to inform remote processor that the address has changed?
=> no reservation mechanism that ensure that you can reuse the same address

case 2) relying on use_default_ept
=> Ensure that both side have always the same addresses to communicate.

>
> I'd rather keep things simple for the refactoring and introduce new features
> later if need be.

Yes I agree with you, but here it could become a nightmare for the remote
processor if the Linux endpoint address is not stable.

Anyway we can consider this as a workaround waiting the extension of the NS
announcement to have a better management of the address exchange on channel
initialization.

Thanks
Arnaud

>
> As I said, it may be that I don't understand the usecase.
>
> Thanks,
> Mathieu
>
>> +}
>> +
>> +static void rpmsg_chrdev_remove(struct rpmsg_device *rpdev)
>> +{
>> + int ret;
>> +
>> + ret = device_for_each_child(&rpdev->dev, NULL, rpmsg_chrdev_eptdev_destroy);
>> + if (ret)
>> + dev_warn(&rpdev->dev, "failed to destroy endpoints: %d\n", ret);
>> +}
>> +
>> +static struct rpmsg_device_id rpmsg_chrdev_id_table[] = {
>> + { .name = RPMSG_CHAR_DEVNAME },
>> + { },
>> +};
>> +
>> +static struct rpmsg_driver rpmsg_chrdev_driver = {
>> + .probe = rpmsg_chrdev_probe,
>> + .remove = rpmsg_chrdev_remove,
>> + .id_table = rpmsg_chrdev_id_table,
>> + .drv = {
>> + .name = "rpmsg_chrdev",
>> + },
>> +};
>> +
>> static int rpmsg_chrdev_init(void)
>> {
>> int ret;
>> @@ -429,16 +465,30 @@ static int rpmsg_chrdev_init(void)
>> rpmsg_class = class_create(THIS_MODULE, "rpmsg");
>> if (IS_ERR(rpmsg_class)) {
>> pr_err("failed to create rpmsg class\n");
>> - unregister_chrdev_region(rpmsg_major, RPMSG_DEV_MAX);
>> - return PTR_ERR(rpmsg_class);
>> + ret = PTR_ERR(rpmsg_class);
>> + goto free_region;
>> + }
>> +
>> + ret = register_rpmsg_driver(&rpmsg_chrdev_driver);
>> + if (ret < 0) {
>> + pr_err("rpmsg: failed to register rpmsg raw driver\n");
>> + goto free_class;
>> }
>>
>> return 0;
>> +
>> +free_class:
>> + class_destroy(rpmsg_class);
>> +free_region:
>> + unregister_chrdev_region(rpmsg_major, RPMSG_DEV_MAX);
>> +
>> + return ret;
>> }
>> postcore_initcall(rpmsg_chrdev_init);
>>
>> static void rpmsg_chrdev_exit(void)
>> {
>> + unregister_rpmsg_driver(&rpmsg_chrdev_driver);
>> class_destroy(rpmsg_class);
>> unregister_chrdev_region(rpmsg_major, RPMSG_DEV_MAX);
>> }
>> --
>> 2.17.1
>>