Re: [PATCH v4 2/2] Embedded USB Debugger (EUD) driver

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On 03/02/2020 19:35, Bjorn Andersson wrote:
On Thu 30 Jan 20:43 PST 2020, Avaneesh Kumar Dwivedi wrote:

Hi Avaneesh.

Please aim for keeping the sort order in this file (ignore QCOM_APR
which obviously is in the wrong place)

+       tristate "QTI Embedded USB Debugger (EUD)"
+       depends on ARCH_QCOM

If we persist with the model of EXTCON you should "select EXTCON" here.

+       help
+         The Embedded USB Debugger (EUD) driver is a driver for the
+         control peripheral which waits on events like USB attach/detach
+         and charger enable/disable. The control peripheral further helps
+         support the USB-based debug and trace capabilities.
+         This module enables support for Qualcomm Technologies, Inc.
+         Embedded USB Debugger (EUD).

Suggest.

This module enables support for Qualcomm Technologies, Inc.
Embedded USB Debugger (EUD).
The EUD is a control peripheral which reports VBUS attach/detach, charger enable/disable and USB-based debug and trace capabilities.


+ * Copyright (c) 2016-2018, The Linux Foundation. All rights reserved.

2020

+
+static int enable_eud(struct eud_chip *priv)
+{
+	int ret;
+
+	/* write into CSR to enable EUD */
+	writel_relaxed(BIT(0), priv->eud_reg_base + EUD_REG_CSR_EUD_EN);
+	/* Enable vbus, chgr & safe mode warning interrupts */
+	writel_relaxed(EUD_INT_VBUS | EUD_INT_CHGR | EUD_INT_SAFE_MODE,
+			priv->eud_reg_base + EUD_REG_INT1_EN_MASK);
+
+	/* Ensure Register Writes Complete */

So... You are writing a register in an on-chip PMIC. The PMIC is responsible for detecting USB ID and supplying VBUS as appropriate.

You then get an interrupt to inform you of the state ?

+static ssize_t enable_store(struct device *dev,
+				struct device_attribute *attr,
+				const char *buf, size_t count)
+{
+	struct eud_chip *chip = dev_get_drvdata(dev);
+	int enable = 0;

You shouldn't need to initialize this as you're checking the return
value of sscanf().

+	int ret = 0;
+
+	if (sscanf(buf, "%du", &enable) != 1)
+		return -EINVAL;
+
+	if (enable == EUD_ENABLE_CMD)
+		ret = enable_eud(chip);

If ret is !0 you should probably return that, rather than count...

+	else if (enable == EUD_DISABLE_CMD)
+		disable_eud(chip);
+	if (!ret)

...and then you don't need this check, or initialize ret to 0 above.

+		chip->enable = enable;

So if I write 42 to "enable" nothing will change in the hardware, but
chip->enable will be 42...

+	return count;
+}

I was just going to comment on usb_connector but, does the above code need a synchronization primitive to serialize with the worker and interrupt handler ?

+static int msm_eud_probe(struct platform_device *pdev)
+{
+	struct eud_chip *chip;
+	struct resource *res;
+	int ret;
+
+	chip = devm_kzalloc(&pdev->dev, sizeof(*chip), GFP_KERNEL);
+	if (!chip)
+		return -ENOMEM;
+
+	chip->dev = &pdev->dev;
+	platform_set_drvdata(pdev, chip);
+
+	chip->extcon = devm_extcon_dev_allocate(&pdev->dev, eud_extcon_cable);

Aren't we moving away from extcon in favor of the usb role switching
thing?

Yes.

For the VBUS notification you could use

usb-role-switch and model the USB connector as a child-node of the dual-role controller.

See:
https://patchwork.kernel.org/cover/11346247/
https://patchwork.kernel.org/patch/11346295/
https://patchwork.kernel.org/patch/11346263/

Avaneesh do you have any kernel code that cares about the charger state ?

What we are suggesting here is dropping extcon and using role-switching but, if you have some other code that cares about EXTCON_CHG_USB_SDP you'd have to do additional work.

But, if I understood the implication of the code above where you write to the PMIC and let it handle VBUS/CHARGER on/off and you are just notified of the state change, you should be fine with usb-role-switching.

---
bod



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