Message-ID: <20220917001618.au7hlduxntj6i4no@builder.lan>
Date:   Fri, 16 Sep 2022 19:16:18 -0500
From:   Bjorn Andersson <andersson@...nel.org>
To:     Souradeep Chowdhury <quic_schowdhu@...cinc.com>
Cc:     Andy Gross <agross@...nel.org>, Rob Herring <robh+dt@...nel.org>,
        Alex Elder <elder@...e.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        Sai Prakash Ranjan <quic_saipraka@...cinc.com>,
        Sibi Sankar <quic_sibis@...cinc.com>,
        Rajendra Nayak <quic_rjendra@...cinc.com>, vkoul@...nel.org
Subject: Re: [PATCH V11 2/7] soc: qcom: dcc: Add driver support for Data
 Capture and Compare unit(DCC)

On Fri, Sep 16, 2022 at 02:20:14PM +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.
> 
> Also added the documentation for debugfs entries and explained
> the functionalities of each debugfs file that has been created
> for dcc.
> 
> The following is the justification of using debugfs interface
> over the other alternatives like sysfs/ioctls
> 
> i) As can be seen from the debugfs attribute descriptions,
> some of the debugfs attribute files here contains multiple
> arguments which needs to be accepted from the user. This goes
> against the design style of sysfs.
> 
> ii) The user input patterns have been made simple and convenient
> in this case with the use of debugfs interface as user doesn't
> need to shuffle between different files to execute one instruction
> as was the case on using other alternatives.
> 

Thanks for fixing up the checkpatch warnings.

I did unfortunately find a few more things as I was looking through this
revision.

> diff --git a/drivers/soc/qcom/dcc.c b/drivers/soc/qcom/dcc.c
> new file mode 100644
> index 0000000..7e07f1a
> --- /dev/null
> +++ b/drivers/soc/qcom/dcc.c
> @@ -0,0 +1,1341 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copneight (c) 2015-2021, The Linex Fnendation. All rights reserved.

Something funny happened to Copneight, Linuex and Fnendation.

Should you perhaps also bump the year to 2022?

> + */
[..]
> +/**
> + * struct dcc_drvdata - configuration information related to a dcc device
> + * @base:	      Base Address of the dcc device
> + * @dev:	      The device attached to the driver data
> + * @mutex:	      Lock to protect access and manipulation of dcc_drvdata
> + * @ram_base:         Base address for the SRAM dedicated for the dcc device

@ram_size missing

> + * @ram_offset:       Offset to the SRAM dedicated for dcc device
> + * @mem_map_ver:      Memory map version of DCC hardware
> + * @ram_cfg:          Used for address limit calculation for dcc
> + * @ram_start:        Starting address of DCC SRAM
> + * @sram_dev:	      Micellaneous device equivalent of dcc SRAM
> + * @cfg_head:	      Points to the head of the linked list of addresses
> + * @dbg_dir:          The dcc debugfs directory under which all the debugfs files are placed
> + * @nr_link_list:     Total number of linkedlists supported by the DCC configuration
> + * @loopoff:          Loop offset bits range for the addresses
> + * @enable:           This contains an array of linkedlist enable flags
> + */
> +struct dcc_drvdata {
> +	void __iomem		*base;
> +	struct device		*dev;
> +	struct mutex		mutex;
> +	void __iomem		*ram_base;
> +	size_t			ram_size;
> +	size_t			ram_offset;
> +	int			mem_map_ver;
> +	phys_addr_t		ram_cfg;
> +	phys_addr_t		ram_start;
> +	struct miscdevice	sram_dev;
> +	struct list_head	*cfg_head;
> +	struct dentry		*dbg_dir;
> +	size_t			nr_link_list;
> +	u8			loopoff;
> +	bool                    *enable;
> +};
[..]
> +static int dcc_read_and_clear(struct dcc_drvdata *drvdata)
> +{
> +	int i;
> +	u32 bus_status;
> +	u32 ll_cfg;
> +	u32 tmp_ll_cfg;
> +
> +	for (i = 0; i < drvdata->nr_link_list; i++) {
> +		if (!drvdata->enable[i])
> +			continue;
> +
> +		bus_status = dcc_ll_readl(drvdata, i, DCC_LL_BUS_ACCESS_STATUS);
> +		if (!bus_status)
> +			continue;
> +
> +		dev_err(drvdata->dev,
> +			"Read access error for list %d err: 0x%x.\n", i, bus_status);

This can be unwrapped, or it would look more natural if you wrapped it
after the string.

You should also drop the '.' at the end of the message.

If you want to shorten it down a little bit more, you could rename
bus_status to status, as there's no ambiguity here.

> +		ll_cfg = dcc_ll_readl(drvdata, i, DCC_LL_CFG);
> +		tmp_ll_cfg = ll_cfg & ~DCC_TRIGGER_MASK;
> +		dcc_ll_writel(drvdata, tmp_ll_cfg, i, DCC_LL_CFG);
> +		dcc_ll_writel(drvdata, DCC_STATUS_MASK, i,
> +			      DCC_LL_BUS_ACCESS_STATUS);

This can be unwrapped.

> +		dcc_ll_writel(drvdata, ll_cfg, i, DCC_LL_CFG);
> +		return -ENODATA;
> +	}
> +
> +	return 0;
> +}
> +
> +static int dcc_sw_trigger(struct dcc_drvdata *drvdata)
> +{
> +	void __iomem *addr;
> +	int ret;
> +	int i;
> +	u32 ll_cfg;
> +	u32 tmp_ll_cfg;
> +	u32 val;
> +
> +	mutex_lock(&drvdata->mutex);
> +
> +	for (i = 0; i < drvdata->nr_link_list; i++) {
> +		if (!drvdata->enable[i])
> +			continue;
> +		ll_cfg = dcc_ll_readl(drvdata, i, DCC_LL_CFG);
> +		tmp_ll_cfg = ll_cfg & ~DCC_TRIGGER_MASK;
> +		dcc_ll_writel(drvdata, tmp_ll_cfg, i, DCC_LL_CFG);
> +		dcc_ll_writel(drvdata, 1, i, DCC_LL_SW_TRIGGER);
> +		dcc_ll_writel(drvdata, ll_cfg, i, DCC_LL_CFG);
> +	}
> +
> +	addr = drvdata->base + DCC_STATUS(drvdata->mem_map_ver);
> +	if (readl_poll_timeout(addr, val, (FIELD_GET(DCC_STATUS_MASK, val) == 0),
> +			       1, STATUS_READY_TIMEOUT)) {
> +		dev_err(drvdata->dev,
> +			"DCC is busy after receiving sw tigger.\n");

Unwrapp this please, and drop the '.' at the end.

> +		ret = -EBUSY;
> +		goto out_unlock;
> +	}
> +
> +	ret = dcc_read_and_clear(drvdata);
> +
> +out_unlock:
> +	mutex_unlock(&drvdata->mutex);
> +	return ret;
> +}
> +
> +static void _dcc_ll_cfg_reset_link(struct dcc_cfg_attr *cfg)
> +{
> +	cfg->addr = 0x00;
> +	cfg->link = 0;
> +	cfg->prev_off = 0;
> +	cfg->prev_addr = cfg->addr;
> +}
> +
> +static void _dcc_emit_read_write(struct dcc_drvdata *drvdata,
> +				 struct dcc_config_entry *entry,
> +				 struct dcc_cfg_attr *cfg)
> +{
> +	if (cfg->link) {
> +		/*
> +		 * write new offset = 1 to continue
> +		 * processing the list
> +		 */
> +
> +		dcc_sram_write_auto(drvdata, cfg->link, &cfg->sram_offset);
> +
> +		/* Reset link and prev_off */
> +		_dcc_ll_cfg_reset_link(cfg);
> +	}
> +
> +	cfg->addr = DCC_RD_MOD_WR_DESCRIPTOR;
> +	dcc_sram_write_auto(drvdata, cfg->addr, &cfg->sram_offset);
> +
> +	dcc_sram_write_auto(drvdata, entry->mask, &cfg->sram_offset);
> +
> +	dcc_sram_write_auto(drvdata, entry->write_val, &cfg->sram_offset);
> +
> +	cfg->addr = 0;
> +}
> +
> +static void _dcc_emit_loop(struct dcc_drvdata *drvdata, struct dcc_config_entry *entry,
> +			   struct dcc_cfg_attr *cfg,
> +			   struct dcc_cfg_loop_attr *cfg_loop,
> +			   u32 *total_len)
> +{
> +	/* Check if we need to write link of prev entry */
> +	if (cfg->link)
> +		dcc_sram_write_auto(drvdata, cfg->link, &cfg->sram_offset);
> +
> +	if (cfg_loop->loop_start) {
> +		cfg_loop->loop = (cfg->sram_offset - cfg_loop->loop_off) / 4;
> +		cfg_loop->loop |= (cfg_loop->loop_cnt << drvdata->loopoff) &
> +		GENMASK(DCC_ADDR_LIMIT, drvdata->loopoff);

Odd line wrap. Please indent better.

> +		cfg_loop->loop |= DCC_LOOP_DESCRIPTOR;
> +		*total_len += (*total_len - cfg_loop->loop_len) * cfg_loop->loop_cnt;
> +
> +		dcc_sram_write_auto(drvdata, cfg_loop->loop, &cfg->sram_offset);
> +
> +		cfg_loop->loop_start = false;
> +		cfg_loop->loop_len = 0;
> +		cfg_loop->loop_off = 0;
> +	} else {
> +		cfg_loop->loop_start = true;
> +		cfg_loop->loop_cnt = entry->loop_cnt - 1;
> +		cfg_loop->loop_len = *total_len;
> +		cfg_loop->loop_off = cfg->sram_offset;
> +	}
> +
> +	/* Reset link and prev_off */
> +	_dcc_ll_cfg_reset_link(cfg);
> +}
> +
> +static void _dcc_emit_write(struct dcc_drvdata *drvdata,
> +			    struct dcc_config_entry *entry,
> +			    struct dcc_cfg_attr *cfg,
> +			    u32 *total_len)
> +{
> +	u32 off;
> +
> +	if (cfg->link) {
> +		/*
> +		 * write new offset = 1 to continue
> +		 * processing the list
> +		 */
> +		dcc_sram_write_auto(drvdata, cfg->link, &cfg->sram_offset);
> +
> +		/* Reset link and prev_off */
> +		cfg->addr = 0x00;
> +		cfg->prev_off = 0;
> +		cfg->prev_addr = cfg->addr;
> +	}
> +
> +	off = entry->offset / 4;
> +	/* write new offset-length pair to correct position */
> +	cfg->link |= ((off & GENMASK(7, 0)) | BIT(15) | ((entry->len << 8) & GENMASK(14, 8)));

Would it be possible to get some defines for these masks and bits?
Perhaps use FIELD_PREP() instead of manually mask and shift the values.

> +	cfg->link |= DCC_LINK_DESCRIPTOR;
> +
> +	/* Address type */
> +	cfg->addr = (entry->base >> 4) & GENMASK(DCC_ADDR_LIMIT, 0);
> +	if (entry->apb_bus)
> +		cfg->addr |= DCC_ADDR_DESCRIPTOR | DCC_WRITE_IND | DCC_APB_IND;
> +	else
> +		cfg->addr |= DCC_ADDR_DESCRIPTOR | DCC_WRITE_IND | DCC_AHB_IND;
> +	dcc_sram_write_auto(drvdata, cfg->addr, &cfg->sram_offset);
> +
> +	dcc_sram_write_auto(drvdata, cfg->link, &cfg->sram_offset);
> +
> +	dcc_sram_write_auto(drvdata, entry->write_val, &cfg->sram_offset);
> +
> +	cfg->addr = 0x00;
> +	cfg->link = 0;
> +}
[..]
> +static ssize_t dcc_config_add_write(struct dcc_drvdata *drvdata, char *buf, int curr_list)
> +{
> +	int ret, bus;
> +	int nval;
> +	unsigned int addr, write_val;
> +	char apb_bus[4];
> +
> +	nval = sscanf(buf, "%x %x %s", &addr, &write_val, apb_bus);
> +
> +	if (nval <= 1 || nval > 3)
> +		return -EINVAL;
> +
> +	if (nval == 3) {
> +		if (!strcmp("apb", apb_bus))
> +			bus = 1;
> +		else if (!strcmp("apb", apb_bus))
> +			bus = 0;
> +		else
> +			return -EINVAL;
> +	}
> +
> +	ret = dcc_add_write(drvdata, addr, write_val, bus, curr_list);

return dcc_add_write(); and you can drop the local variable.

> +
> +	return ret;
> +}
> +
> +static ssize_t config_read(struct file *filp, char __user *userbuf,
> +			   size_t count, loff_t *ppos)
> +{
> +	struct dcc_drvdata *drvdata = filp->private_data;
> +	struct dcc_config_entry *entry;
> +	char local_buf[64], buf[100] = "\0";
> +	int len = 0, tot_len = 0, index = 0, curr_list;
> +
> +	mutex_lock(&drvdata->mutex);
> +	curr_list = dcc_filp_curr_list(filp);
> +	if (curr_list < 0)
> +		return curr_list;
> +
> +	list_for_each_entry(entry,
> +			    &drvdata->cfg_head[curr_list], list) {
> +		index++;
> +		switch (entry->desc_type) {
> +		case DCC_READ_WRITE_TYPE:
> +			len = snprintf(local_buf, 64,
> +				       "Index: 0x%x, mask: 0x%x, val: 0x%x\n",

Wouldn't it be nice if this matches the format used to specify the
instructions?

I.e. "RW <addr> <value> <mask>"

> +				       index, entry->mask, entry->write_val);
> +			break;
> +		case DCC_LOOP_TYPE:
> +			len = snprintf(local_buf, 64, "Index: 0x%x, Loop: %d\n",
> +				       index, entry->loop_cnt);
> +			break;
> +		case DCC_WRITE_TYPE:
> +			len = snprintf(local_buf, 64,
> +				       "Write Index: 0x%x, Base: 0x%x, Offset: 0x%x, len: 0x%x APB: %d\n",
> +				       index, entry->base, entry->offset, entry->len,
> +				       entry->apb_bus);
> +			break;
> +		case DCC_READ_TYPE:
> +			len = snprintf(local_buf, 64,
> +				       "Read Index: 0x%x, Base: 0x%x, Offset: 0x%x, len: 0x%x APB: %d\n",

Can't this generate something like:
  Read Index: 0x1, Base: 0xaabbccdd, Offset: 0xaa, len: 0xaa APB: 1
Afaict that's 65 bytes.

If that's the case you will end up with tot_len > strlen(buf). You
probably meant to use scnprintf(), which would return 63.

But either way, the tail would be chopped of.

> +				       index, entry->base, entry->offset,
> +				       entry->len, entry->apb_bus);
> +		}
> +		tot_len += len;
> +		strlcat(buf, local_buf, sizeof(local_buf));

The limit should be the destination buffer, i.e. sizeof(buf).

But why is sizeof(buf) only 100? If you have a RMW in there you will fit
1.5 entries in the buffer.


I think it would be better to use single_open() and use the seq_file()
interface for generating your data. That will handle the buffer
management for you, among other things.

> +	}
> +	mutex_unlock(&drvdata->mutex);
> +	return simple_read_from_buffer(userbuf, count, ppos, buf, tot_len);
> +}
> +
> +static ssize_t config_write(struct file *filp,
> +			    const char __user *user_buf, size_t count,
> +			    loff_t *ppos)
> +{
> +	int ret, curr_list;
> +	char *token, buf[50];
> +	char *delim = " ";
> +	struct dcc_drvdata *drvdata = filp->private_data;
> +
> +	ret = copy_from_user(buf, user_buf, count);

count might be > sizeof(buf).

> +	if (ret)
> +		return -EFAULT;
> +
> +	curr_list = dcc_filp_curr_list(filp);
> +	if (curr_list < 0)
> +		return curr_list;
> +
> +	if (buf[count - 1] == '\n')

count can be 0.

> +		buf[count - 1] = '\0';

buf[] might not be \n or NUL-terminated.

> +
> +	token = strsep((char **)&buf, delim);
> +
> +	if (!strcmp("R", token)) {
> +		ret = dcc_config_add_read(drvdata, buf, curr_list);
> +	} else if (!strcmp("W", token)) {
> +		ret = dcc_config_add_write(drvdata, buf, curr_list);
> +	} else if (!strcmp("RW", token)) {
> +		ret = dcc_config_add_read_write(drvdata, buf, curr_list);
> +	} else if (!strcmp("L", token)) {
> +		ret = dcc_config_add_loop(drvdata, buf, curr_list);
> +	} else {
> +		dev_err(drvdata->dev, "%s is not a correct input\n", token);
> +		return -EINVAL;
> +	}
[..]
> +static ssize_t dcc_sram_read(struct file *file, char __user *data,
> +			     size_t len, loff_t *ppos)
> +{
> +	unsigned char *buf;
> +	struct dcc_drvdata *drvdata = container_of(file->private_data,
> +		struct dcc_drvdata,
> +		sram_dev);
> +
> +	/* EOF check */
> +	if (*ppos > drvdata->ram_size)
> +		return 0;
> +
> +	if ((*ppos + len) > drvdata->ram_size)
> +		len = (drvdata->ram_size - *ppos);

If *ppos == drvdata->ram_size, the EOF check will miss that and len will
be 0.

> +
> +	buf = kzalloc(len, GFP_KERNEL);
> +	if (!buf)
> +		return -ENOMEM;
> +
> +	memcpy_fromio(buf, drvdata->ram_base + *ppos, len);
> +
> +	if (copy_to_user(data, buf, len)) {
> +		kfree(buf);
> +		return -EFAULT;
> +	}
> +
> +	*ppos += len;
> +
> +	kfree(buf);
> +
> +	return len;
> +}
> +

Regards,
Bjorn

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