Thanks Pierre,
On 06/05/2022 15:13, Pierre-Louis Bossart wrote:
On 5/6/22 03:47, Srinivas Kandagatla wrote:
Currently timeout for autoenumeration during probe and bus reset is set to
2 secs which is really a big value. This can have an adverse effect on
boot time if the slave device is not ready/reset.
This was the case with wcd938x which was not reset yet but we spent 2
secs waiting in the soundwire controller probe. Reduce this time to
1/10 of Hz which should be good enough time to finish autoenumeration
if any slaves are available on the bus.
Humm, now that I think of it I am not sure what reducing the timeout does.
It's clear that autoenumeration should be very fast, but if there is
nothing to enumerate what would happen then? It seems that reducing the
timeout value only forces an inconsistent configuration to be exposed
earlier, but that would not result in a functional change where the
missing device would magically appear, would it? Is this change mainly
to make the tests fail faster? If the 'slave device is not ready/reset',
is there a recovery mechanism to recheck later?
Would you mind clarifying what happens after the timeout, and why the
timeout would happen in the first place?
This issue is mostly present/seen with WCD938x codec due to its Linux
device model.
WCD938x Codec has 3 Linux component drivers
1. TX Component (A soundwire device connected to TX Soundwire Master)
2. RX Component (A soundwire device connected to RX Soundwire Master)
3. Master Component (Linux component framework master for (1) and (2)
and registers ASoC codec)
Also we have only one reset for (1) and (2).
reset line is handled by (3)
There are two possibilities when the WCD938x reset can happen,
1. If reset happens earlier than probing (1) and (2) which is best case.
2. if reset happens after (1) and (2) are probed then SoundWire TX and
RX master will have spend 2 + 2 secs waiting, Which is a long time out
Hence the patch.
TBH, the 2 sec timeout value was just a random number which I added at
the start, we had to come up with some sensible value over the time
anyway for that.
You could say why do we need wait itself in the first place.
The reason we need wait in first place is because, there is a danger of
codec accessing registers even before enumeration is finished. Because
most of the ASoC codec registration happens as part of codec/component
driver probe function rather than status callback.
I hope this answers your questions.
thanks,
--srini
Thanks!
Reported-by: Srinivasa Rao Mandadapu <quic_srivasam@xxxxxxxxxxx>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
---
Changes since v1:
replaced HZ/10 with 100 as suggested by Pierre
drivers/soundwire/qcom.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/soundwire/qcom.c b/drivers/soundwire/qcom.c
index 7367aa88b8ac..d6111f69d320 100644
--- a/drivers/soundwire/qcom.c
+++ b/drivers/soundwire/qcom.c
@@ -105,7 +105,7 @@
#define SWRM_SPECIAL_CMD_ID 0xF
#define MAX_FREQ_NUM 1
-#define TIMEOUT_MS (2 * HZ)
+#define TIMEOUT_MS 100
#define QCOM_SWRM_MAX_RD_LEN 0x1
#define QCOM_SDW_MAX_PORTS 14
#define DEFAULT_CLK_FREQ 9600000
