[S] Change in flashrom[main]: serial: Fix sp_flush_incoming for serprog TCP connections

[Anastasia Klimchuk (Code Review)]

Attention is currently required from: Stanislav Ponomarev.

Anastasia Klimchuk has posted comments on this change. ( https://review.coreboot.org/c/flashrom/+/79112?usp=email )

Change subject: serial: Fix sp_flush_incoming for serprog TCP connections
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Patch Set 2:

(10 comments)

Commit Message:

https://review.coreboot.org/c/flashrom/+/79112/comment/fb1cbbc2_c157a4b1 :
PS2, Line 9: pet
maybe remove "pet" :)

https://review.coreboot.org/c/flashrom/+/79112/comment/d8c511d4_c19fff25 :
PS2, Line 9: I was working on an
During the development of

https://review.coreboot.org/c/flashrom/+/79112/comment/bc61d4c4_ebd18b6a :
PS2, Line 10: when i implemented
implementation of

https://review.coreboot.org/c/flashrom/+/79112/comment/6f375d08_fe6d1e03 :
PS2, Line 11: i
uppercase

https://review.coreboot.org/c/flashrom/+/79112/comment/8b5d3424_7b66fe1c :
PS2, Line 14: I added
This patch adds

https://review.coreboot.org/c/flashrom/+/79112/comment/7667ca81_fcec0ab7 :
PS2, Line 18: After that
TESTED=

Patchset:

PS2: 
Thank you for you patch! I added some comments.

I really like your original commit message, it explains everything very well. But I added few comments on it, just because typically commit message is written is more formal style (since it stays in git history forever).

Also when I got an email about this patch, it does not have display name (literally email from "Name of user not set"). I think it's probably display name or full name in Gerrit account is empty, or both. You can set it to anything, any nickname is fine.

File serial.c:

https://review.coreboot.org/c/flashrom/+/79112/comment/67cf5fda_70113442 :
PS2, Line 380: int ret = tcflush(sp_fd, TCIFLUSH);
             : 	if (ret == 0)
             : 		return;
We typically use more compact variation. I don't see this exact ret value is used again, so you can do like this:

if (!tcflush(sp_fd, TCIFLUSH))
    	return;

https://review.coreboot.org/c/flashrom/+/79112/comment/a4ad7027_d311b8db :
PS2, Line 392: ret > 0
A question about return codes: `serialport_read_nonblock` can return positive or negative error codes, I am wondering does positive return code reliably indicates that no more data available to read? I just read through the comment and the code of `serialport_read_nonblock` and I can't decide on that :)

If it works reliably, maybe you can add a bit longer comment, like "Positive error code indicates no more data available, which is normal situation and means flush completed successfully".

https://review.coreboot.org/c/flashrom/+/79112/comment/9d204200_bfbf6988 :
PS2, Line 401: return;
I am thinking, maybe change slightly with less returns. It's harder to read when every second line returns.

if (errno == ENOTTY) {
   <... serialport_read_nonblock loop ...>
   if (ret < 0)
    msg_perr("Could not flush serial port incoming buffer: read has failed");
  } else {
   msg_perr_strerror("Could not flush serial port incoming buffer: ");
  }