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;