linux-kernel - Re: [PATCH v2 3/7] soc: qcom: add QCOM PBS driver

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Date:   Wed, 26 Jul 2023 17:36:08 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Anjelique Melendez <quic_amelende@...cinc.com>, pavel@....cz,
        lee@...nel.org, thierry.reding@...il.com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        agross@...nel.org, andersson@...nel.org
Cc:     luca.weiss@...rphone.com, u.kleine-koenig@...gutronix.de,
        quic_subbaram@...cinc.com, linux-leds@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-pwm@...r.kernel.org
Subject: Re: [PATCH v2 3/7] soc: qcom: add QCOM PBS driver

On 25.07.2023 21:34, Anjelique Melendez wrote:
> Add the Qualcomm PBS (Programmable Boot Sequencer) driver. The QCOM PBS
> driver supports configuring software PBS trigger events through PBS RAM
> on Qualcomm Technologies, Inc (QTI) PMICs.
> 
> Signed-off-by: Anjelique Melendez <quic_amelende@...cinc.com>
> ---
[...]

> +
> +	u32			base;
> +};
> +
> +static int qcom_pbs_read(struct pbs_dev *pbs, u32 address, u8 *val)
> +{
> +	int ret;
> +
> +	address += pbs->base;
Any reason not to just keep the base address in struct pbs_dev and use
normal regmap r/w helpers?

[...]

> +
> +static int qcom_pbs_wait_for_ack(struct pbs_dev *pbs, u8 bit_pos)
> +{
> +	u16 retries = 2000, delay = 1000;
> +	int ret;
> +	u8 val;
> +
> +	while (retries--) {
> +		ret = qcom_pbs_read(pbs, PBS_CLIENT_SCRATCH2, &val);
> +		if (ret < 0)
> +			return ret;
> +
> +		if (val == 0xFF) {
This should be a constant, not a magic value

> +			/* PBS error - clear SCRATCH2 register */
> +			ret = qcom_pbs_write(pbs, PBS_CLIENT_SCRATCH2, 0);
> +			if (ret < 0)
> +				return ret;
> +
> +			dev_err(pbs->dev, "NACK from PBS for bit %u\n", bit_pos);
> +			return -EINVAL;
> +		}
> +
> +		if (val & BIT(bit_pos)) {
> +			dev_dbg(pbs->dev, "PBS sequence for bit %u executed!\n", bit_pos);
> +			break;
> +		}
> +
> +		usleep_range(delay, delay + 100);
So worst case scenario this will wait for over 2 seconds?

> +	}
> +
> +	if (!retries) {
> +		dev_err(pbs->dev, "Timeout for PBS ACK/NACK for bit %u\n", bit_pos);
> +		return -ETIMEDOUT;
> +	}
> +
> +	return 0;
return 0 instead of break above?

> +}
> +
> +/**
> + * qcom_pbs_trigger_event() - Trigger the PBS RAM sequence
> + * @pbs: Pointer to PBS device
> + * @bitmap: bitmap
> + *
> + * This function is used to trigger the PBS RAM sequence to be
> + * executed by the client driver.
> + *
> + * The PBS trigger sequence involves
> + * 1. setting the PBS sequence bit in PBS_CLIENT_SCRATCH1
> + * 2. Initiating the SW PBS trigger
> + * 3. Checking the equivalent bit in PBS_CLIENT_SCRATCH2 for the
> + *    completion of the sequence.
> + * 4. If PBS_CLIENT_SCRATCH2 == 0xFF, the PBS sequence failed to execute
> + *
> + * Returns: 0 on success, < 0 on failure
> + */
> +int qcom_pbs_trigger_event(struct pbs_dev *pbs, u8 bitmap)
> +{
> +	u8 val, mask;
> +	u16 bit_pos;
> +	int ret;
> +
> +	if (!bitmap) {
> +		dev_err(pbs->dev, "Invalid bitmap passed by client\n");
> +		return -EINVAL;
> +	}
> +
> +	if (IS_ERR_OR_NULL(pbs))
> +		return -EINVAL;
> +
> +	mutex_lock(&pbs->lock);
> +	ret = qcom_pbs_read(pbs, PBS_CLIENT_SCRATCH2, &val);
> +	if (ret < 0)
> +		goto out;
> +
> +	if (val == 0xFF) {
> +		/* PBS error - clear SCRATCH2 register */
> +		ret = qcom_pbs_write(pbs, PBS_CLIENT_SCRATCH2, 0);
> +		if (ret < 0)
> +			goto out;
> +	}
> +
> +	for (bit_pos = 0; bit_pos < 8; bit_pos++) {
> +		if (bitmap & BIT(bit_pos)) {
> +			/*
> +			 * Clear the PBS sequence bit position in
> +			 * PBS_CLIENT_SCRATCH2 mask register.
> +			 */
Don't think the "in the X register" parts are useful.

> +			ret = qcom_pbs_masked_write(pbs, PBS_CLIENT_SCRATCH2, BIT(bit_pos), 0);
> +			if (ret < 0)
> +				goto error;
> +
> +			/*
> +			 * Set the PBS sequence bit position in
> +			 * PBS_CLIENT_SCRATCH1 register.
> +			 */
> +			val = mask = BIT(bit_pos);
You're using mask/val for half the function calls..
Stick with one approach.

[...]

> +struct pbs_dev *get_pbs_client_device(struct device *dev)
> +{
> +	struct device_node *pbs_dev_node;
> +	struct platform_device *pdev;
> +	struct pbs_dev *pbs;
> +
> +	pbs_dev_node = of_parse_phandle(dev->of_node, "qcom,pbs", 0);
> +	if (!pbs_dev_node) {
> +		dev_err(dev, "Missing qcom,pbs property\n");
> +		return ERR_PTR(-ENODEV);
> +	}
> +
> +	pdev = of_find_device_by_node(pbs_dev_node);
> +	if (!pdev) {
> +		dev_err(dev, "Unable to find PBS dev_node\n");
> +		pbs = ERR_PTR(-EPROBE_DEFER);
> +		goto out;
> +	}
> +
> +	pbs = platform_get_drvdata(pdev);
> +	if (!pbs) {
This check seems unnecessary, the PBS driver would have had to fail
probing if set_drvdata never got called.

Konrad