linux-kernel - Re: [PATCH V2 1/1] greybus: gb-beagleplay: Remove use of pad bytes

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Date:   Tue, 12 Dec 2023 20:00:52 +0530
From:   Ayush Singh <ayushdevel1325@...il.com>
To:     Alex Elder <elder@...e.org>, greybus-dev@...ts.linaro.org
Cc:     johan@...nel.org, elder@...nel.org, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, jkridner@...gleboard.org, nm@...com,
        yujie.liu@...el.com
Subject: Re: [PATCH V2 1/1] greybus: gb-beagleplay: Remove use of pad bytes


On 12/12/23 19:31, Alex Elder wrote:
> On 12/11/23 12:54 AM, Ayush Singh wrote:
>> Make gb-beagleplay greybus spec compliant by moving cport information to
>> transport layer instead of using `header->pad` bytes.
>>
>> Greybus HDLC frame now has the following payload:
>> 1. le16 cport
>> 2. gb_operation_msg_hdr msg_header
>> 3. u8 *msg_payload
>>
>> Fixes: ec558bbfea67 ("greybus: Add BeaglePlay Linux Driver")
>> Signed-off-by: Ayush Singh <ayushdevel1325@...il.com>
>
> I would say that this is an improvement, but I wish I
> had a better picture in mind of how this works.  The
> initial commit provided some explanation, but even
> there it talks about the "CC1352 (running SVC Zephyr
> application)" and that leads me to wonder even how
> the hardware is structured.  (I'm not really asking
> you for this right now, but you have a reference to
> something that provides some background, you should
> provide it for context.)

Yes, I am thinking of revamping the Beagle connect docs to reflect the 
new architecture with some charts and provide a better overall picture. 
It is sorely needed at this point.


> Another general comment is that the use of HDLC seems
> like it could be a more clearly separated layer that
> could be used by other Greybus protocols or applications.
> Maybe that's overkill, but it is a distinct layer, right?

Initial commits of gb-beagleplay did separate all the HDLC parts from 
the driver. However, it was decided to keep it together and maybe 
extract it in the future if other drivers need it.


>
> I had a comment or two about using (void *) instead of
> (u8 *), to reduce the need for explicit type casts.  But
> I found that (u8 *) is used elsewhere in the Greybus code.
>
> One comment I *will* share is that the serdev RX callback
> has a const receive buffer.  I recommend you preserve that
> "constness" in your code.
>
>                     -Alex

The constness of the receive buffer is actually preserved. The 
`gb_tty_receive` function calls `hdlc_rx` (which takes const u8 *). This 
function copies the data to a separate buffer 
(`gb_beagleplay->rx_buffer`) for further processing. So the const data 
is not modified.


Ayush Singh