On Mon, 13 May 2024, Hans de Goede wrote:
> On 5/13/24 3:34 PM, Ilpo Järvinen wrote:
> > On Mon, 13 May 2024, Hans de Goede wrote:
> >> On 5/13/24 3:14 PM, Ilpo Järvinen wrote:
> >>> On Mon, 13 May 2024, Hans de Goede wrote:
> >>>> On 5/13/24 2:12 PM, Ilpo Järvinen wrote:
> >>>>> On Mon, 13 May 2024, Hans de Goede wrote:
> >>>>>> On 5/13/24 10:34 AM, Ilpo Järvinen wrote:
> >>>>>>> On Sun, 12 May 2024, Hans de Goede wrote:
> >>>
> >>>>>>>> +
> >>>>>>>> + dell_bl->resp_idx++;
> >>>>>>>> + if (dell_bl->resp_idx < dell_bl->resp_len)
> >>>>>>>> + continue;
> >>>>>>>> +
> >>>>>>>> + csum = dell_uart_checksum(dell_bl->resp, dell_bl->resp_len - 1);
> >>>>>>>> + if (dell_bl->resp[dell_bl->resp_len - 1] != csum) {
> >>>>>>>> + dev_err(dell_bl->dev, "Checksum mismatch got 0x%02x expected 0x%02x\n",
> >>>>>>>> + dell_bl->resp[dell_bl->resp_len - 1], csum);
> >>>>>>>> + dell_bl->status = -EIO;
> >>>>>>>> + goto wakeup;
> >>>>>>>> + }
> >>>>>>>
> >>>>>>> Why is the checksum calculation and check inside the loop??
> >>>>>>
> >>>>>> The loop iterates over received bytes, which may contain extra data
> >>>>>> after the response, the:
> >>>>>>
> >>>>>> dell_bl->resp_idx++;
> >>>>>> if (dell_bl->resp_idx < dell_bl->resp_len)
> >>>>>> continue;
> >>>>>>
> >>>>>> continues looping until we have received all the expected bytes. So here, past this
> >>>>>> check, we are are at the point where we have a complete response and then we verify it.
> >>>>>>
> >>>>>> And on successful verification wake-up any waiters.
> >>>>>
> >>>>> So effectively you want to terminate the loop on two conditions here:
> >>>>>
> >>>>> a) dell_bl->resp_idx == dell_bl->resp_len (complete frame)
> >>>>> a) if i == len (not yet received a full frame)
> >>>>>
> >>>>> Why not code those rather than the current goto & continue madness?
> >>>>>
> >>>>> Then, after the loop, you can test:
> >>>>>
> >>>>> if (dell_bl->resp_idx == dell_bl->resp_len) {
> >>>>> // calc checksum, etc.
> >>>>> }
> >>>>>
> >>>>> ?
> >>>>
> >>>> Ok, I've added the following change for v3:
> >>>>
> >>>> diff --git a/drivers/platform/x86/dell/dell-uart-backlight.c b/drivers/platform/x86/dell/dell-uart-backlight.c
> >>>> index bf5b12efcb19..66d8c6ddcb83 100644
> >>>> --- a/drivers/platform/x86/dell/dell-uart-backlight.c
> >>>> +++ b/drivers/platform/x86/dell/dell-uart-backlight.c
> >>>> @@ -87,6 +87,7 @@ static int dell_uart_bl_command(struct dell_uart_backlight *dell_bl,
> >>>> dell_bl->status = -EBUSY;
> >>>> dell_bl->resp = resp;
> >>>> dell_bl->resp_idx = 0;
> >>>> + dell_bl->resp_len = -1; /* Invalid / unset */
> >>>> dell_bl->resp_max_len = resp_max_len;
> >>>> dell_bl->pending_cmd = cmd[1];
> >>>>
> >>>> @@ -219,7 +219,7 @@ static size_t dell_uart_bl_receive(struct serdev_device *serdev, const u8 *data,
> >>>> return len;
> >>>> }
> >>>>
> >>>> - for (i = 0; i < len; i++) {
> >>>> + for (i = 0; i < len && dell_bl->resp_idx != dell_bl->resp_len; i++, dell_bl->resp_idx++) {
> >>>> dell_bl->resp[dell_bl->resp_idx] = data[i];
> >>>>
> >>>> switch (dell_bl->resp_idx) {
> >>>> @@ -228,46 +228,41 @@ static size_t dell_uart_bl_receive(struct serdev_device *serdev, const u8 *data,
> >>>> if (dell_bl->resp_len < MIN_RESP_LEN) {
> >>>> dev_err(dell_bl->dev, "Response length too small %d < %d\n",
> >>>> dell_bl->resp_len, MIN_RESP_LEN);
> >>>> - dell_bl->status = -EIO;
> >>>> - goto wakeup;
> >>>> + goto error;
> >>>> }
> >>>>
> >>>> if (dell_bl->resp_len > dell_bl->resp_max_len) {
> >>>> dev_err(dell_bl->dev, "Response length too big %d > %d\n",
> >>>> dell_bl->resp_len, dell_bl->resp_max_len);
> >>>> - dell_bl->status = -EIO;
> >>>> - goto wakeup;
> >>>> + goto error;
> >>>> }
> >>>> break;
> >>>> case RESP_CMD: /* CMD byte */
> >>>> if (dell_bl->resp[RESP_CMD] != dell_bl->pending_cmd) {
> >>>> dev_err(dell_bl->dev, "Response cmd 0x%02x != pending 0x%02x\n",
> >>>> dell_bl->resp[RESP_CMD], dell_bl->pending_cmd);
> >>>> - dell_bl->status = -EIO;
> >>>> - goto wakeup;
> >>>> + goto error;
> >>>> }
> >>>> break;
> >>>> }
> >>>> + }
> >>>>
> >>>> - dell_bl->resp_idx++;
> >>>> - if (dell_bl->resp_idx < dell_bl->resp_len)
> >>>> - continue;
> >>>> -
> >>>> + if (dell_bl->resp_idx == dell_bl->resp_len) {
> >>>> csum = dell_uart_checksum(dell_bl->resp, dell_bl->resp_len - 1);
> >>>> if (dell_bl->resp[dell_bl->resp_len - 1] != csum) {
> >>>> dev_err(dell_bl->dev, "Checksum mismatch got 0x%02x expected 0x%02x\n",
> >>>> dell_bl->resp[dell_bl->resp_len - 1], csum);
> >>>> - dell_bl->status = -EIO;
> >>>> - goto wakeup;
> >>>> + goto error;
> >>>> }
> >>>> -
> >>>> dell_bl->status = 0; /* Success */
> >>>> - goto wakeup;
> >>>> + wake_up(&dell_bl->wait_queue);
> >>>> + return i;
> >>>> }
> >>>>
> >>>> return len;
> >>>>
> >>>> -wakeup:
> >>>> +error:
> >>>> + dell_bl->status = -EIO;
> >>>> wake_up(&dell_bl->wait_queue);
> >>>> return i + 1;
> >>>> }
> >>>
> >>> Thanks, this is way easier to follow.
> >>
> >> I'm glad you like it.
> >>
> >> There is a little bug in this version though, the goto error on the checksum fail
> >> case returns i + i, which should be i in that case, I'll just drop the goto there and
> >> instead always use the return i already present at the end of the
> >> "if (dell_bl->resp_idx == dell_bl->resp_len) { }" block.
> >
> > It could have been solved more logically incrementing i and resp_idx here:
> >
> > dell_bl->resp[dell_bl->resp_idx] = data[i];
> > dell_bl->resp_idx++;
> > i++;
> >
> > so that the inconsistent state is eliminated.
> >
> > I also realized (I know I was the one who suggested it) that reverse logic
> > would be better for the incomplete frame check:
> >
> > if (dell_bl->resp_idx < dell_bl->resp_len)
> > return len;
> >
> > // checksum logic...
> >
> > Perhaps the success and error return paths could then be merged too.
>
> Interesting suggestion, I also realized that the 2 response-length checks are a
> range check so I've folded those together. So here is what I have now for v3,
> note that the i++ is now done when copying data over:
>
> i = 0;
> while (i < len && dell_bl->resp_idx != dell_bl->resp_len) {
> dell_bl->resp[dell_bl->resp_idx] = data[i++];
>
> switch (dell_bl->resp_idx) {
> case RESP_LEN: /* Length byte */
> dell_bl->resp_len = dell_bl->resp[RESP_LEN];
> if (!in_range(dell_bl->resp_len, MIN_RESP_LEN, dell_bl->resp_max_len)) {
in_range() takes start and len, not start and end. I really hate that
helper because it has that trap and would often require "+ min" to be
added.
> dev_err(dell_bl->dev, "Response length %d out if range %d - %d\n",
> dell_bl->resp_len, MIN_RESP_LEN, dell_bl->resp_max_len);
> dell_bl->status = -EIO;
> goto wakeup;
> }
> break;
> case RESP_CMD: /* CMD byte */
> if (dell_bl->resp[RESP_CMD] != dell_bl->pending_cmd) {
> dev_err(dell_bl->dev, "Response cmd 0x%02x != pending 0x%02x\n",
> dell_bl->resp[RESP_CMD], dell_bl->pending_cmd);
> dell_bl->status = -EIO;
> goto wakeup;
> }
> break;
> }
> dell_bl->resp_idx++;
Good, I didn't realize the switch used the index.
--
i.
> }
>
> if (dell_bl->resp_idx != dell_bl->resp_len)
> return len; /* Response not complete yet */
>
> csum = dell_uart_checksum(dell_bl->resp, dell_bl->resp_len - 1);
> if (dell_bl->resp[dell_bl->resp_len - 1] == csum) {
> dell_bl->status = 0; /* Success */
> } else {
> dev_err(dell_bl->dev, "Checksum mismatch got 0x%02x expected 0x%02x\n",
> dell_bl->resp[dell_bl->resp_len - 1], csum);
> dell_bl->status = -EIO;
> }
> wakeup:
> wake_up(&dell_bl->wait_queue);
> return i;
> }
>
> Regards,
>
> Hans
>
>
