[PATCH] fsi: occ: Improve response status checking
Eddie James
eajames at linux.ibm.com
Tue Feb 1 02:29:10 AEDT 2022
On 1/30/22 23:56, Joel Stanley wrote:
> On Mon, 10 Jan 2022 at 15:58, Eddie James <eajames at linux.ibm.com> wrote:
>> If the driver sequence number coincidentally equals the previous
>> command response sequence number, the driver may proceed with
>> fetching the entire buffer before the OCC has processed the current
>> command. To be sure the correct response is obtained, check the
>> command type and also retry if any of the response parameters have
>> changed when the rest of the buffer is fetched.
>>
>> Signed-off-by: Eddie James <eajames at linux.ibm.com>
>> ---
>> drivers/fsi/fsi-occ.c | 63 ++++++++++++++++++++++++++++++-------------
>> 1 file changed, 44 insertions(+), 19 deletions(-)
>>
>> diff --git a/drivers/fsi/fsi-occ.c b/drivers/fsi/fsi-occ.c
>> index 7eaab1be0aa4..67569282dd69 100644
>> --- a/drivers/fsi/fsi-occ.c
>> +++ b/drivers/fsi/fsi-occ.c
>> @@ -451,6 +451,15 @@ static int occ_trigger_attn(struct occ *occ)
>> return rc;
>> }
>>
>> +static void fsi_occ_print_timeout(struct occ *occ, struct occ_response *resp,
>> + u8 seq_no, u8 cmd_type)
>> +{
>> + dev_err(occ->dev,
>> + "resp timeout status=%02x seq=%d cmd=%d, our seq=%d cmd=%d\n",
>> + resp->return_status, resp->seq_no, resp->cmd_type, seq_no,
>> + cmd_type);
>> +}
>> +
>> int fsi_occ_submit(struct device *dev, const void *request, size_t req_len,
>> void *response, size_t *resp_len)
>> {
>> @@ -461,12 +470,14 @@ int fsi_occ_submit(struct device *dev, const void *request, size_t req_len,
>> struct occ_response *resp = response;
>> size_t user_resp_len = *resp_len;
>> u8 seq_no;
>> + u8 cmd_type;
>> u16 checksum = 0;
>> u16 resp_data_length;
>> const u8 *byte_request = (const u8 *)request;
>> - unsigned long start;
>> + unsigned long end;
>> int rc;
>> size_t i;
>> + bool retried = false;
>>
>> *resp_len = 0;
>>
>> @@ -478,6 +489,8 @@ int fsi_occ_submit(struct device *dev, const void *request, size_t req_len,
>> return -EINVAL;
>> }
>>
>> + cmd_type = byte_request[1];
>> +
>> /* Checksum the request, ignoring first byte (sequence number). */
>> for (i = 1; i < req_len - 2; ++i)
>> checksum += byte_request[i];
>> @@ -509,30 +522,30 @@ int fsi_occ_submit(struct device *dev, const void *request, size_t req_len,
>> if (rc)
>> goto done;
>>
>> - /* Read occ response header */
>> - start = jiffies;
>> +retry:
>> + end = jiffies + timeout;
>> do {
>> + /* Read occ response header */
>> rc = occ_getsram(occ, 0, resp, 8);
>> if (rc)
>> goto done;
>>
>> if (resp->return_status == OCC_RESP_CMD_IN_PRG ||
>> resp->return_status == OCC_RESP_CRIT_INIT ||
>> - resp->seq_no != seq_no) {
>> - rc = -ETIMEDOUT;
>> -
>> - if (time_after(jiffies, start + timeout)) {
>> - dev_err(occ->dev, "resp timeout status=%02x "
>> - "resp seq_no=%d our seq_no=%d\n",
>> - resp->return_status, resp->seq_no,
>> - seq_no);
>> + resp->seq_no != seq_no || resp->cmd_type != cmd_type) {
> You're testing for two different types of conditions. The first is
> when the SBE is busy doing something else:
>
> if (resp->return_status == OCC_RESP_CMD_IN_PRG ||
> resp->return_status == OCC_RESP_CRIT_INIT ||
>
> And the others are when the message is not for the current user:
>
> resp->seq_no != seq_no || resp->cmd_type != cmd_type) {
>
> Should we be separating them out? It makes sense that the first means
> we should keep trying. For the second case should we bail straight
> away, instead of waiting for the timeout?
They're really the same thing actually. If the sequence number or
command type is incorrect, it means the OCC is processing a different
command, and we need to wait for it to get to our command.
>
> How often do we see one vs the other?
>
>> + if (time_after(jiffies, end)) {
>> + fsi_occ_print_timeout(occ, resp, seq_no,
>> + cmd_type);
>> + rc = -ETIMEDOUT;
>> goto done;
>> }
>>
>> set_current_state(TASK_UNINTERRUPTIBLE);
>> schedule_timeout(wait_time);
>> + } else {
>> + break;
>> }
>> - } while (rc);
>> + } while (true);
> Use while (true) instead of do { } while (true) to make it clearer
> what's going on. Or refactor it to put the time_after in the while(),
> as this is what the loop is waiting on.
OK, I went in circles (pun intended) working on this loop, but I'll try
and make it look better.
>
>> /* Extract size of response data */
>> resp_data_length = get_unaligned_be16(&resp->data_length);
>> @@ -543,17 +556,29 @@ int fsi_occ_submit(struct device *dev, const void *request, size_t req_len,
>> goto done;
>> }
>>
>> - dev_dbg(dev, "resp_status=%02x resp_data_len=%d\n",
>> - resp->return_status, resp_data_length);
>> -
>> - /* Grab the rest */
>> + /* Now get the entire response; get header again in case it changed */
>> if (resp_data_length > 1) {
>> - /* already got 3 bytes resp, also need 2 bytes checksum */
>> - rc = occ_getsram(occ, 8, &resp->data[3], resp_data_length - 1);
>> + rc = occ_getsram(occ, 0, resp, resp_data_length + 7);
>> if (rc)
>> goto done;
>> +
>> + if (resp->return_status == OCC_RESP_CMD_IN_PRG ||
>> + resp->return_status == OCC_RESP_CRIT_INIT ||
>> + resp->seq_no != seq_no || resp->cmd_type != cmd_type) {
>> + if (!retried) {
>> + retried = true;
>> + goto retry;
> Not sure about this.
>
> How often did this situation come up?
>
> Did you consider instead returning an error here?
Well I can't say it's frequent, but hitting this condition was what
drove making this change in the first place. It needs to be handled.
Previously if this occurrred, we got a checksum error, so it effectively
already returned an error.
>
>> + }
>> +
>> + fsi_occ_print_timeout(occ, resp, seq_no, cmd_type);
>> + rc = -ETIMEDOUT;
>> + goto done;
>> + }
>> }
>>
>> + dev_dbg(dev, "resp_status=%02x resp_data_len=%d\n",
>> + resp->return_status, resp_data_length);
>> +
>> occ->client_response_size = resp_data_length + 7;
>> rc = occ_verify_checksum(occ, resp, resp_data_length);
>>
>> @@ -598,7 +623,7 @@ static int occ_probe(struct platform_device *pdev)
>> occ->version = (uintptr_t)of_device_get_match_data(dev);
>> occ->dev = dev;
>> occ->sbefifo = dev->parent;
>> - occ->sequence_number = 1;
>> + occ->sequence_number = (u8)((jiffies % 0xff) + 1);
> This is interesting. You didn't mention this in the commit message;
> you're trying to get a random number for the sequence number?
Yea, this reduces the chances of hitting that retry above. If it's
always 1, then every time the driver is bound it tries the first command
with the same sequence number. This is a problem when FSI scanning with
the host already running, as the driver gets unbound/rebound several
times in a row, and we easily hit the checksum problem, since we proceed
to get the full response even though it's not for the latest command,
and then the buffer is updated at the same time. So using a non-zero
random number is very helpful.
Thanks,
Eddie
>
>> mutex_init(&occ->occ_lock);
>>
>> if (dev->of_node) {
>> --
>> 2.27.0
>>
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