linux-kernel - Re: [PATCH V1 2/3] drivers: misc: dcc: Add driver support for Data Capture and Compare unit(DCC)

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Message-ID: <ZDo4jIIV7cfPD2qW@kroah.com>
Date:   Sat, 15 Apr 2023 07:39:24 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Souradeep Chowdhury <quic_schowdhu@...cinc.com>
Cc:     Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, Alex Elder <elder@...e.org>,
        Arnd Bergmann <arnd@...db.de>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        Sibi Sankar <quic_sibis@...cinc.com>,
        Rajendra Nayak <quic_rjendra@...cinc.com>
Subject: Re: [PATCH V1 2/3] drivers: misc: dcc: Add driver support for Data
 Capture and Compare unit(DCC)

On Fri, Apr 14, 2023 at 07:29:12PM +0530, Souradeep Chowdhury wrote:
> The DCC is a DMA Engine designed to capture and store data
> during system crash or software triggers. The DCC operates
> based on user inputs via the debugfs interface. The user gives
> addresses as inputs and these addresses are stored in the
> dcc sram. In case of a system crash or a manual software
> trigger by the user through the debugfs interface,
> the dcc captures and stores the values at these addresses.
> This patch contains the driver which has all the methods
> pertaining to the debugfs interface, auxiliary functions to
> support all the four fundamental operations of dcc namely
> read, write, read/modify/write and loop. The probe method
> here instantiates all the resources necessary for dcc to
> operate mainly the dedicated dcc sram where it stores the
> values. The DCC driver can be used for debugging purposes
> without going for a reboot since it can perform software
> triggers as well based on user inputs.

You have 72 columns, why not use them all please?

> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (c) 2015-2021, The Linux Foundation. All rights reserved.
> + * Copyright (c) 2022, Qualcomm Innovation Center, Inc. All rights reserved.

It is now 2023 :)




> + */
> +
> +#include <linux/bitfield.h>
> +#include <linux/bitops.h>
> +#include <linux/debugfs.h>
> +#include <linux/delay.h>
> +#include <linux/fs.h>
> +#include <linux/io.h>
> +#include <linux/iopoll.h>
> +#include <linux/miscdevice.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <linux/platform_device.h>
> +#include <linux/slab.h>
> +#include <linux/uaccess.h>
> +
> +#define STATUS_READY_TIMEOUT		5000  /* microseconds */
> +
> +#define DCC_SRAM_NODE "dcc_sram"

You only use this once, why is a #define needed?

> +static void dcc_create_debug_dir(struct dcc_drvdata *drvdata)
> +{
> +	int i;
> +	char list_num[10];
> +	struct dentry *list;
> +	struct device *dev = drvdata->dev;
> +
> +	drvdata->dbg_dir = debugfs_create_dir(dev_name(dev), NULL);

You are creating a directory at the root of debugfs with just your
device name?  While that will work, that feels very odd.  Please use a
subdirectory.

> +	if (IS_ERR(drvdata->dbg_dir)) {
> +		pr_err("can't create debugfs dir\n");

There is no need to ever check the return value of a debugfs call.

Nor do you really ever even need to save off the dentry here, just look
it up when you need to remove it.

> +		return;
> +	}
> +
> +	for (i = 0; i <= drvdata->nr_link_list; i++) {
> +		sprintf(list_num, "%d", i);
> +		list = debugfs_create_dir(list_num, drvdata->dbg_dir);
> +		debugfs_create_file("enable", 0600, list, drvdata, &enable_fops);
> +		debugfs_create_file("config", 0600, list, drvdata, &config_fops);
> +	}
> +
> +	debugfs_create_file("trigger", 0200, drvdata->dbg_dir, drvdata, &trigger_fops);
> +	debugfs_create_file("ready", 0400, drvdata->dbg_dir, drvdata, &ready_fops);
> +	debugfs_create_file("config_reset", 0200, drvdata->dbg_dir,
> +			    drvdata, &config_reset_fops);

This really looks like you are using debugfs to control the device, not
just for debugging information.  How are you going to be able to use the
device in a system that has debugfs disabled?

thanks,

greg k-h