linux-kernel - Re: [PATCH] soundwire: qcom: update status from device id 1

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Date:   Fri, 16 Sep 2022 11:39:39 +0200
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        vkoul@...nel.org
Cc:     alsa-devel@...a-project.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org, sanyog.r.kale@...el.com,
        yung-chuan.liao@...ux.intel.com, quic_srivasam@...cinc.com
Subject: Re: [PATCH] soundwire: qcom: update status from device id 1



On 9/16/22 11:12, Srinivas Kandagatla wrote:
> 
> 
> On 15/09/2022 14:10, Pierre-Louis Bossart wrote:
>>
>>
>> On 9/15/22 14:42, Srinivas Kandagatla wrote:
>>> By default autoenumeration is enabled on QCom SoundWire controller
>>> which means the core should not be dealing with device 0 w.r.t
>>> enumeration.
>>> Currently device 0 status is also shared with SoundWire core which
>>> confuses
>>> the core sometimes and we endup adding 0:0:0:0 slave device.
>>
>> The change looks fine, but the description of the issue is surprising.
> 
> Thanks Pierre,
> 
>>
>> Whether autoenumeration is enabled or not is irrelevant, by spec the
>> device0 cannot be in ALERT status and throw in-band interrupts to the
>> host with this mechanism.
> 
> This issue is more of around enumeration stage in specific during device
> status change interrupt from controller. Sharing the device 0 status
> with core makes it think that there is a device with 0:0:0:0 address and
> it tries to park device to group 13.
Still not clear, sorry, see my comment below.

> 
> 
> --srini
> 
>>
>>> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
>>> ---
>>>   drivers/soundwire/qcom.c | 4 ++--
>>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/soundwire/qcom.c b/drivers/soundwire/qcom.c
>>> index e21a3306bf01..871e4d8b32c7 100644
>>> --- a/drivers/soundwire/qcom.c
>>> +++ b/drivers/soundwire/qcom.c
>>> @@ -428,7 +428,7 @@ static int
>>> qcom_swrm_get_alert_slave_dev_num(struct qcom_swrm_ctrl *ctrl)
>>>         ctrl->reg_read(ctrl, SWRM_MCP_SLV_STATUS, &val);
>>>   -    for (dev_num = 0; dev_num <= SDW_MAX_DEVICES; dev_num++) {
>>> +    for (dev_num = 1; dev_num <= SDW_MAX_DEVICES; dev_num++) {
>>>           status = (val >> (dev_num * SWRM_MCP_SLV_STATUS_SZ));
>>>             if ((status & SWRM_MCP_SLV_STATUS_MASK) ==
>>> SDW_SLAVE_ALERT) {

can this really happen?

Device0 cannot be in alert status, can it? The only this it can do is
assert PREQ and set the Device0 status to 1 (ATTACHED). I don't get how
a device status could be 2.

So even if the status is shared somehow,I don't see how this could be
related to parking the device as suggested above. If the condition is
always false then changing the loop counter from 0 to 1 would not have
an effect?


>>> @@ -448,7 +448,7 @@ static void qcom_swrm_get_device_status(struct
>>> qcom_swrm_ctrl *ctrl)
>>>       ctrl->reg_read(ctrl, SWRM_MCP_SLV_STATUS, &val);
>>>       ctrl->slave_status = val;
>>>   -    for (i = 0; i <= SDW_MAX_DEVICES; i++) {
>>> +    for (i = 1; i <= SDW_MAX_DEVICES; i++) {
>>>           u32 s;
>>>             s = (val >> (i * 2));