Messages in this thread | | | Date | Fri, 2 Dec 2022 10:19:19 +0000 | Subject | Re: [PATCH 2/3] soundwire: cadence: Remove wasted space in response_buf | From | Richard Fitzgerald <> |
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On 01/12/2022 18:12, Pierre-Louis Bossart wrote: > > > On 12/1/22 07:48, Richard Fitzgerald wrote: >> The response_buf was declared much larger (128 entries) than the number >> of responses that could ever be written into it (maximum 8). > > Indeed I don't know why we used 128 entries. This is a magic value that > doesn't appear in any specs I've looked at. > > Note that there's 'sniffer' mode when each response takes two > consecutive 32-words in the FIFO. we've never used this mode though so > it's not really an issue. > > It's also possible that this is related to the automatic command retry, > where a failed command can be re-issued 15 times. However in that case > the worst case would be 32 commands * 15 = 480. The value of 128 makes > no sense at all, unless it was an upper bound for 8 * 15. We don't use > this hardware retry btw. > > See more below... > >> Reduce response_buf to 8 entries and add checking in cdns_read_response() >> to prevent overflowing reponse_buf if CDNS_MCP_RX_FIFO_AVAIL contains >> an unexpectedly large number. >> >> Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com> >> --- >> drivers/soundwire/cadence_master.c | 6 ++++++ >> drivers/soundwire/cadence_master.h | 2 +- >> 2 files changed, 7 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/soundwire/cadence_master.c b/drivers/soundwire/cadence_master.c >> index 27699f341f2c..95c84d9f0775 100644 >> --- a/drivers/soundwire/cadence_master.c >> +++ b/drivers/soundwire/cadence_master.c >> @@ -774,8 +774,14 @@ static void cdns_read_response(struct sdw_cdns *cdns) >> u32 num_resp, cmd_base; >> int i; >> >> + BUILD_BUG_ON(ARRAY_SIZE(cdns->response_buf) < CDNS_MCP_CMD_LEN); >> + >> num_resp = cdns_readl(cdns, CDNS_MCP_FIFOSTAT); >> num_resp &= CDNS_MCP_RX_FIFO_AVAIL; >> + if (num_resp > ARRAY_SIZE(cdns->response_buf)) { >> + dev_warn(cdns->dev, "RX AVAIL %d too long\n", num_resp); >> + num_resp = CDNS_MCP_CMD_LEN; > > .... this is different from what the hardware documentation tells me. > The range of values to RX_FIFO_AVAIL is 0..RX_FIFO_DEPTH + 2. > > I don't understand the +2, but we should maybe be more cautious and use > u32 response_buf[CDNS_MCP_CMD_LEN + 2]; >
Probably we wouldn't know what to do with those extra 2 responses. _cdns_xfer_msg() tells cdns_fill_msg_resp() to extract the same number of responses as the original message length. So it would only extract 8 maximum. But anyway yes I can add the mysterious +2 into this. Thinking about it, that's probably a good idea anyay for the next patch that drains the RX FIFO after an error.
>> + } >> >> cmd_base = CDNS_MCP_CMD_BASE; >> >> diff --git a/drivers/soundwire/cadence_master.h b/drivers/soundwire/cadence_master.h >> index 0434d70d4b1f..c2d817e8e22a 100644 >> --- a/drivers/soundwire/cadence_master.h >> +++ b/drivers/soundwire/cadence_master.h >> @@ -117,7 +117,7 @@ struct sdw_cdns { >> struct sdw_bus bus; >> unsigned int instance; >> >> - u32 response_buf[0x80]; >> + u32 response_buf[8]; >> struct completion tx_complete; >> struct sdw_defer *defer; >>
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