linux-kernel - Re: [PATCH 05/19] soundwire: amd: add soundwire interrupt handling

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Message-ID: <ff99cf26-56df-a3ae-ca0d-691d0cb034fc@linux.intel.com>
Date:   Wed, 11 Jan 2023 09:19:57 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Vijendar Mukunda <Vijendar.Mukunda@....com>, broonie@...nel.org,
        vkoul@...nel.org, alsa-devel@...a-project.org
Cc:     Basavaraj.Hiregoudar@....com, Sunil-kumar.Dommati@....com,
        Mario.Limonciello@....com, Mastan.Katragadda@....com,
        arungopal.kondaveeti@....com,
        Bard Liao <yung-chuan.liao@...ux.intel.com>,
        Sanyog Kale <sanyog.r.kale@...el.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 05/19] soundwire: amd: add soundwire interrupt handling




>  
> +static void amd_sdwc_process_ping_status(u64 response, struct amd_sdwc_ctrl *ctrl)
> +{
> +	u64 slave_stat = 0;
> +	u32 val = 0;
> +	u16 dev_index;
> +
> +	/* slave status from ping response*/

response */

> +	slave_stat = FIELD_GET(AMD_SDW_MCP_SLAVE_STAT_0_3, response);
> +	slave_stat |= FIELD_GET(AMD_SDW_MCP_SLAVE_STAT_4_11, response) << 8;
> +
> +	dev_dbg(ctrl->dev, "%s: slave_stat:0x%llx\n", __func__, slave_stat);
> +	for (dev_index = 0; dev_index <= SDW_MAX_DEVICES; ++dev_index) {
> +		val = (slave_stat >> (dev_index * 2)) & AMD_SDW_MCP_SLAVE_STATUS_MASK;
> +		dev_dbg(ctrl->dev, "%s val:0x%x\n", __func__, val);
> +		switch (val) {
> +		case SDW_SLAVE_ATTACHED:
> +			ctrl->status[dev_index] = SDW_SLAVE_ATTACHED;
> +			break;
> +		case SDW_SLAVE_UNATTACHED:
> +			ctrl->status[dev_index] = SDW_SLAVE_UNATTACHED;
> +			break;
> +		case SDW_SLAVE_ALERT:
> +			ctrl->status[dev_index] = SDW_SLAVE_ALERT;
> +			break;
> +		default:
> +			ctrl->status[dev_index] = SDW_SLAVE_RESERVED;
> +			break;
> +		}
> +	}
> +}
> +
> +static void amd_sdwc_read_and_process_ping_status(struct amd_sdwc_ctrl *ctrl)
> +{
> +	u64 response = 0;
> +
> +	mutex_lock(&ctrl->bus.msg_lock);
> +	response = amd_sdwc_send_cmd_get_resp(ctrl, 0, 0);
> +	mutex_unlock(&ctrl->bus.msg_lock);
> +	amd_sdwc_process_ping_status(response, ctrl);

Is this saying that you actually need to send a PING frame manually
every time the manager needs to check the device status, including
interrupts?

> +}
> +
>  static u32 amd_sdwc_read_ping_status(struct sdw_bus *bus)
>  {
>  	struct amd_sdwc_ctrl *ctrl = to_amd_sdw(bus);
> @@ -1132,6 +1173,119 @@ static int amd_sdwc_register_dais(struct amd_sdwc_ctrl *ctrl)
>  					       dais, num_dais);
>  }
>  
> +static void amd_sdwc_update_slave_status_work(struct work_struct *work)
> +{
> +	struct amd_sdwc_ctrl *ctrl =
> +		container_of(work, struct amd_sdwc_ctrl, amd_sdw_work);
> +	u32 sw_status_change_mask_0to7_reg;
> +	u32 sw_status_change_mask_8to11_reg;
> +
> +	switch (ctrl->instance) {
> +	case ACP_SDW0:
> +		sw_status_change_mask_0to7_reg = SW_STATE_CHANGE_STATUS_MASK_0TO7;
> +		sw_status_change_mask_8to11_reg = SW_STATE_CHANGE_STATUS_MASK_8TO11;
> +		break;
> +	case ACP_SDW1:
> +		sw_status_change_mask_0to7_reg = P1_SW_STATE_CHANGE_STATUS_MASK_0TO7;
> +		sw_status_change_mask_8to11_reg = P1_SW_STATE_CHANGE_STATUS_MASK_8TO11;
> +		break;
> +	default:
> +		dev_err(ctrl->dev, "Invalid Soundwire controller instance\n");
> +		return;
> +	}
> +
> +	if (ctrl->status[0] == SDW_SLAVE_ATTACHED) {
> +		acp_reg_writel(0, ctrl->mmio + sw_status_change_mask_0to7_reg);
> +		acp_reg_writel(0, ctrl->mmio + sw_status_change_mask_8to11_reg);
> +	}
> +
> +update_status:
> +	sdw_handle_slave_status(&ctrl->bus, ctrl->status);
> +	if (ctrl->status[0] == SDW_SLAVE_ATTACHED) {
> +		acp_reg_writel(AMD_SDW_IRQ_MASK_0TO7, ctrl->mmio + sw_status_change_mask_0to7_reg);
> +		acp_reg_writel(AMD_SDW_IRQ_MASK_8TO11,
> +			       ctrl->mmio + sw_status_change_mask_8to11_reg);
> +		amd_sdwc_read_and_process_ping_status(ctrl);
> +		goto update_status;
> +	}

well no, you have to use some sort of retry count. You cannot handle
interrupts in a loop like this, a faulty or chatty device would keep
signaling an issue and you would be stuck here for a while.

In addition, it's not clear if this is really needed. We added this loop
in cadence_master.c because of issues with multiple devices becoming
attached at the same time and how the hardware works. As it turns out,
this update_status loop seems to be a paranoid case, the actually cause
for devices de-attaching was found by Cirrus Logic and fixed in
"soundwire: cadence: fix updating slave status when a bus has multiple
peripherals"

You would need to explain how the status is detected and if any race
conditions can occur.