linux-kernel - Re: [PATCH v2] rpmsg: char: Export alias for RPMSG ID rpmsg-raw from table

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Message-ID: <aF13mM9PSvTnKQ1k@p14s>
Date: Thu, 26 Jun 2025 10:38:48 -0600
From: Mathieu Poirier <mathieu.poirier@...aro.org>
To: Andrew Davis <afd@...com>
Cc: Bjorn Andersson <andersson@...nel.org>, Hari Nagalla <hnagalla@...com>,
	Beleswar Padhi <b-padhi@...com>, linux-remoteproc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] rpmsg: char: Export alias for RPMSG ID rpmsg-raw from
 table

On Wed, Jun 25, 2025 at 12:12:03PM -0500, Andrew Davis wrote:
> On 6/25/25 11:13 AM, Mathieu Poirier wrote:
> > Good day,
> > 
> > On Thu, Jun 19, 2025 at 03:57:22PM -0500, Andrew Davis wrote:
> > > Module aliases are used by userspace to identify the correct module to
> > > load for a detected hardware. The currently supported RPMSG device IDs for
> > > this module include "rpmsg-raw", but the module alias is "rpmsg_chrdev".
> > > 
> > > Use the helper macro MODULE_DEVICE_TABLE(rpmsg) to export the correct
> > > supported IDs. And while here, to keep backwards compatibility we also add
> > > the other ID "rpmsg_chrdev" so that it is also still exported as an alias.
> > > 
> > > This has the side benefit of adding support for some legacy firmware
> > > which still uses the original "rpmsg_chrdev" ID. This was the ID used for
> > > this driver before it was upstreamed (as reflected by the module alias).
> > 
> > I was surprised to receive this patch - my question from almost a year back is
> > still pending.
> > 
> 
> I answered[0] your question and never received any follow up questions so I had
> assumed the answer was satisfactory.
>

Ah!  I never saw your reply, apologies for that.
 
> > > 
> > > Signed-off-by: Andrew Davis <afd@...com>
> > > Acked-by: Hari Nagalla <hnagalla@...com>
> > > Tested-by: Hari Nagalla <hnagalla@...com>
> > > ---
> > > 
> > > Changes for v2:
> > >   - Rebased on v6.16-rc1
> > >   - Added Acked/Tested-by
> > > 
> > > [v1] https://www.spinics.net/lists/linux-remoteproc/msg18959.html
> > > 
> > >   drivers/rpmsg/rpmsg_char.c | 3 ++-
> > >   1 file changed, 2 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
> > > index eec7642d26863..96fcdd2d7093c 100644
> > > --- a/drivers/rpmsg/rpmsg_char.c
> > > +++ b/drivers/rpmsg/rpmsg_char.c
> > > @@ -522,8 +522,10 @@ static void rpmsg_chrdev_remove(struct rpmsg_device *rpdev)
> > >   static struct rpmsg_device_id rpmsg_chrdev_id_table[] = {
> > >   	{ .name	= "rpmsg-raw" },
> > > +	{ .name	= "rpmsg_chrdev" },
> > >   	{ },
> > >   };
> > > +MODULE_DEVICE_TABLE(rpmsg, rpmsg_chrdev_id_table);
> > 
> > ... and I still don't understand why this patch is needed.  What is broken that
> > this patch fixes?
> > 
> 
> Today when this driver is built as a module it does not automatically load
> when a matching firmware is started. You can see examples of documentation
> working around this by manually loading it[1] and even applications
> attempting the same in code[2]. This should not be needed. Here is why
> this happens and how this patch fixes it:
> 
> A given firmware that makes use of this driver will have one of two
> RPMSG device IDs: "rpmsg-raw" or "rpmsg_chrdev". Let's look at each in
> turn:
> 
> If the ID is "rpmsg_chrdev" then this driver module will be loaded into
> the kernel (that is what the MODULE_ALIAS line below did). But it will
> not cause the driver module to probe, as probe is triggered by a match
> in the above rpmsg_device_id table.
> 
> If the ID is "rpmsg-raw" then this driver module will probe with the
> firmware, but only if this driver module was already loaded into the
> kernel, or was built-in to the kernel.
> 
> By adding "rpmsg_chrdev" to the table we make this driver probe for
> firmware with that ID. And by adding MODULE_DEVICE_TABLE we make both
> IDs trigger the module to be loaded if it has not been already.
> 
> This patch makes it so both IDs do both needed actions. Where before
> each ID would only do one action, but not the other.

The part I was missing is the call to add_uevent_var() that uses @rpdev->id.name
in rpmsg_uevent() - with that in mind it makes sense.  I have applied your
patch.

Thanks,
Mathieu

> 
> Andrew
> 
> [0] https://www.spinics.net/lists/linux-remoteproc/msg19814.html
> [1] https://github.com/OpenAMP/openamp-system-reference/blob/main/examples/linux/rpmsg-mat-mul/README.md?plain=1#L42
> [2] https://github.com/Xilinx/meta-openamp/blob/master/recipes-openamp/rpmsg-examples/rpmsg-mat-mul/mat_mul_demo.c#L306
> 
> > Thanks,
> > Mathieu
> > 
> > >   static struct rpmsg_driver rpmsg_chrdev_driver = {
> > >   	.probe = rpmsg_chrdev_probe,
> > > @@ -565,6 +567,5 @@ static void rpmsg_chrdev_exit(void)
> > >   }
> > >   module_exit(rpmsg_chrdev_exit);
> > > -MODULE_ALIAS("rpmsg:rpmsg_chrdev");
> > >   MODULE_DESCRIPTION("RPMSG device interface");
> > >   MODULE_LICENSE("GPL v2");
> > > -- 
> > > 2.39.2
> > >