linux-kernel - Re: [PATCH] soc: hisilicon: Support HCCS driver on Kunpeng SoC

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Message-Id: <e0c4f4b5-8b34-4542-b676-f98ddb8ef586@app.fastmail.com>
Date:   Mon, 24 Apr 2023 10:09:47 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Huisong Li" <lihuisong@...wei.com>,
        "Bjorn Andersson" <andersson@...nel.org>,
        "Matthias Brugger" <matthias.bgg@...il.com>,
        "AngeloGioacchino Del Regno" 
        <angelogioacchino.delregno@...labora.com>,
        "Shawn Guo" <shawnguo@...nel.org>
Cc:     linux-kernel@...r.kernel.org, soc@...nel.org,
        wanghuiqiang@...wei.com, tanxiaofei@...wei.com,
        liuyonglong@...wei.com, huangdaode@...wei.com,
        linux-acpi@...r.kernel.org, "Len Brown" <lenb@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        devicetree@...r.kernel.org, "Rob Herring" <robh+dt@...nel.org>,
        "Frank Rowand" <frowand.list@...il.com>,
        "Krzysztof Kozlowski" <krzysztof.kozlowski+dt@...aro.org>
Subject: Re: [PATCH] soc: hisilicon: Support HCCS driver on Kunpeng SoC

On Mon, Apr 24, 2023, at 09:30, Huisong Li wrote:

> diff --git a/drivers/soc/hisilicon/Kconfig 
> b/drivers/soc/hisilicon/Kconfig
> new file mode 100644
> index 000000000000..81768d47f572
> --- /dev/null
> +++ b/drivers/soc/hisilicon/Kconfig
> @@ -0,0 +1,18 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +
> +menu "Hisilicon SoC drivers"
> +	depends on ARCH_HISI
> +
> +config KUNPENG_HCCS
> +	tristate "HCCS driver on Kunpeng SoC"
> +	depends on ARM64 && ACPI

Is there a compile-time dependency on ARM64? If not, it would
be good to allow compile testing. At the same time, you
can probably tighten this to ARCH_HISI instead of ARM64,
since no other vendors are going to use it:

       depends on ACPI
       depends on (ARM64 && ARCH_HISI) || COMPILE_TEST

> +
> +#include "kunpeng_hccs.h"
> +
> +/* PCC defines */
> +#define HCCS_PCC_SIGNATURE_MASK		0x50434300
> +#define HCCS_PCC_STATUS_CMD_COMPLETE	BIT(0)

Should these perhaps be in include/acpi/pcc.h? The 0x50434300
number is just "PCC\0", so it appears to not be HCCS specific.

> +
> +static int hccs_get_device_property(struct hccs_dev *hdev)
> +{
> +	struct device *dev = hdev->dev;
> +
> +	if (device_property_read_u32(dev, "device-flags", &hdev->flags)) {
> +		dev_err(hdev->dev, "no device-flags property.\n");
> +		return -ENODEV;
> +	}
> +
> +	if (device_property_read_u8(dev, "pcc-type", &hdev->type)) {
> +		dev_err(hdev->dev, "no pcc-type property.\n");
> +		return -ENODEV;
> +	}
> +
> +	if (device_property_read_u32(dev, "pcc-chan-id", &hdev->chan_id)) {
> +		dev_err(hdev->dev, "no pcc-channel property.\n");
> +		return -ENODEV;
> +	}
> +
> +	hdev->intr_mode = hccs_get_bit(hdev->flags, HCCS_DEV_FLAGS_INTR_B);
> +	if (!hccs_dev_property_supported(hdev))
> +		return -EOPNOTSUPP;
> +

Where are the device properties documented? I'm never quite sure how
to handle these for ACPI-only drivers, since we don't normally have the
bindings in Documentation/devicetree/bindings/, but it feels like there
should be some properly reviewed document somewhere else.

Adding ACPI and devicetree maintainers to Cc for clarification. 

> +static int hccs_check_chan_cmd_complete(struct hccs_dev *hdev)
> +{
> +	struct hccs_mbox_client_info *cl_info = &hdev->cl_info;
> +	struct acpi_pcct_shared_memory *comm_base = cl_info->pcc_comm_addr;
> +	u16 status;
> +	int ret;
> +
> +	/*
> +	 * Poll PCC status register every 3us(delay_us) for maximum of
> +	 * deadline_us(timeout_us) until PCC command complete bit is set(cond)
> +	 */
> +	ret = readw_relaxed_poll_timeout(&comm_base->status, status,
> +					 status & HCCS_PCC_STATUS_CMD_COMPLETE,
> +					 HCCS_POLL_STATUS_TIME_INTERVAL_US,
> +					 cl_info->deadline_us);

Is it both safe and faster to use a relaxed readw here, compared
to the normal one? If there is any access to shared memory
involved, you need the implied barrier for serialization, and since this
is already a sleeping operation, I would guess that you don't care
about the last nanosecond of latency here.

> +static ssize_t hccs_show(struct kobject *k, struct attribute *attr, 
> char *buf)
> +{
> +	struct kobj_attribute *kobj_attr;
> +
> +	kobj_attr = container_of(attr, struct kobj_attribute, attr);
> +
> +	return kobj_attr->show(k, kobj_attr, buf);
> +}
> +
> +static const struct sysfs_ops hccs_comm_ops = {
> +	.show = hccs_show,
> +};

Every sysfs interface needs to be documented in Documentation/ABI/

> diff --git a/drivers/soc/hisilicon/kunpeng_hccs.h 
> b/drivers/soc/hisilicon/kunpeng_hccs.h
> new file mode 100644
> index 000000000000..ca557ef115ea
> --- /dev/null
> +++ b/drivers/soc/hisilicon/kunpeng_hccs.h
> @@ -0,0 +1,204 @@
> +/* SPDX-License-Identifier: GPL-2.0+ */
> +/* Copyright (c) 2023 Hisilicon Limited. */
> +
> +#ifndef __KUNPENG_HCCS_H__
> +#define __KUNPENG_HCCS_H__

Are you planning to add more drivers that share this file? If not,
just fold the contents into the driver itself.

     Arnd