linux-kernel - Re: [PATCH] soundwire: qcom: allow multi-link on newer devices

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Date:   Wed, 29 Nov 2023 11:07:20 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Vinod Koul <vkoul@...nel.org>,
        Bard Liao <yung-chuan.liao@...ux.intel.com>,
        Sanyog Kale <sanyog.r.kale@...el.com>,
        linux-arm-msm@...r.kernel.org, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org
Cc:     Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH] soundwire: qcom: allow multi-link on newer devices



On 11/29/23 10:43, Krzysztof Kozlowski wrote:
> On 28/11/2023 16:35, Pierre-Louis Bossart wrote:
>>>  static enum sdw_command_response qcom_swrm_xfer_msg(struct sdw_bus *bus,
>>>  						    struct sdw_msg *msg)
>>>  {
>>> @@ -1078,6 +1090,7 @@ static const struct sdw_master_port_ops qcom_swrm_port_ops = {
>>>  };
>>>  
>>>  static const struct sdw_master_ops qcom_swrm_ops = {
>>> +	.read_prop = qcom_swrm_read_prop,
>>
>> nit-pick: read_prop() literally means "read platform properties".
>>
>> The functionality implemented in this callback looks more like an
>> initialization done in a probe, no?
> 
> Yes, but multi_link is being set by sdw_bus_master_add() just before
> calling read_prop(). It looks a bit odd, because "bus" comes from the
> caller and is probably zero-ed already. Therefore I assumed the code did
> it on purpose - ignored multi_link set before sdw_bus_master_add(),

On the Intel side, there's a bit of luck here.

The caller intel_link_probe() does not set the multi-link property, but
it's set in intel_link_startup() *AFTER* reading the properties - but we
don't have any properties related to multi-link, only the ability to
discard specific links.

>>>  	.xfer_msg = qcom_swrm_xfer_msg,
>>>  	.pre_bank_switch = qcom_swrm_pre_bank_switch,
>>>  	.post_bank_switch = qcom_swrm_post_bank_switch,
>>> @@ -1196,6 +1209,15 @@ static int qcom_swrm_stream_alloc_ports(struct qcom_swrm_ctrl *ctrl,
>>>  
>>>  	mutex_lock(&ctrl->port_lock);
>>>  	list_for_each_entry(m_rt, &stream->master_list, stream_node) {
>>
>> just realizing this now, are you sure the 'port_lock' is the proper
>> means to protecting the stream->master_list? I don't see this used
>> anywhere else in stream.c. I think you need to use bus_lock.
> 
> This is from ctrl, internal driver structure:
> 
> struct qcom_swrm_ctrl *ctrl

My point what that all other instances where list_for_each_entry() is
used on stream->master list rely on the bus_lock.

You may be fine in this specific case with a QCOM-specific lock, not
sure if there's any risk. At any rate that is not introduced by this
patch, so for now

Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>