[greybus-dev] Re: [RFC PATCH v2 11/12] greybus: cpc: honour remote's RX window

On Fri Nov 14, 2025 at 10:07 AM EST, Damien Riégel wrote:

+/**

• • cpc_header_get_frames_acked_count() - Get frames to be acknowledged.
• • @seq: Current sequence number of the endpoint.
• • @ack: Acknowledge number of the received frame.
• • Return: Frames to be acknowledged.
• */

+u8 cpc_header_get_frames_acked_count(u8 seq, u8 ack) +{

• u8 frames_acked_count;
• /* Find number of frames acknowledged with ACK number. */
• if (ack > seq) {

• frames_acked_count = ack - seq;
  

• } else {

• frames_acked_count = 256 - seq;
  

• frames_acked_count += ack;
  

• }
• return frames_acked_count;

+}

There is no need to check whether `ack > seq` since the return value in downcasted to a `u8`. For example, if `ack=0` and `seq=254`, we can simply do `(u8)(0-254)=2`.

+static void __cpc_protocol_receive_ack(struct cpc_cport *cport, u8 recv_wnd, u8 ack) +{

• struct gb_host_device *gb_hd = cport->cpc_hd->gb_hd;
• struct sk_buff *skb;
• u8 acked_frames;
• cport->tcb.send_wnd = recv_wnd;

Little bit of a nitpick, but handling the RX window update in `__cpc_protocol_receive_ack` seems a bit misleading to me, in the sense that the ACK itself is not directly related to the window.

I would either rename the function to indicate that we are handling all the CPort's metadata received from the CPC header, or I would move the RX window update to the caller.

Thanks,