Date:   Tue, 6 Mar 2018 09:21:40 -0700
From:   Lina Iyer <ilina@...eaurora.org>
To:     Stephen Boyd <sboyd@...nel.org>
Cc:     andy.gross@...aro.org, david.brown@...aro.org,
        linux-arm-msm@...r.kernel.org, linux-soc@...r.kernel.org,
        rnayak@...eaurora.org, bjorn.andersson@...aro.org,
        linux-kernel@...r.kernel.org,
        Mahesh Sivasubramanian <msivasub@...eaurora.org>
Subject: Re: [PATCH v4 1/2] drivers: qcom: add command DB driver

On Mon, Mar 05 2018 at 11:42 -0700, Stephen Boyd wrote:
>Quoting Lina Iyer (2018-02-26 09:58:01)
>> diff --git a/drivers/soc/qcom/cmd-db.c b/drivers/soc/qcom/cmd-db.c
>> new file mode 100644
>> index 000000000000..0792a2a98fc9
>> --- /dev/null
>> +++ b/drivers/soc/qcom/cmd-db.c
>> @@ -0,0 +1,319 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +/* Copyright (c) 2016-2018, The Linux Foundation. All rights reserved. */
>> +
>> +#include <linux/kernel.h>
>> +#include <linux/of.h>
>> +#include <linux/of_address.h>
>> +#include <linux/of_platform.h>
>> +#include <linux/of_reserved_mem.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/types.h>
>> +
>> +#include <soc/qcom/cmd-db.h>
>> +
>> +#define NUM_PRIORITY           2
>> +#define MAX_SLV_ID             8
>> +#define CMD_DB_MAGIC           0x0C0330DBUL
>
>Make this an array so it's endian safe.
>
>> +#define SLAVE_ID_MASK          0x7
>> +#define SLAVE_ID_SHIFT         16
>> +
>> +#define ENTRY_HEADER(hdr)      ((void *)cmd_db_header +        \
>> +                               sizeof(*cmd_db_header) +        \
>> +                               hdr->header_offset)
>> +
>> +#define RSC_OFFSET(hdr, ent)   ((void *)cmd_db_header +        \
>> +                               sizeof(*cmd_db_header) +        \
>> +                               hdr.data_offset + ent.offset)
>> +
>> +/**
>> + * entry_header: header for each entry in cmddb
>
>struct entry_header - header for each...
>
Ok

>> + *
>> + * @id: resource's identifier
>> + * @priority: unused
>> + * @addr: the address of the resource
>> + * @len: length of the data
>> + * @offset: offset at which data starts
>
>offset from this entry header at which data starts? Or offset from
>where?
>
Offset from @data_offset of the rsc_header.

>> + */
>> +struct entry_header {
>> +       u64 id;
>> +       u32 priority[NUM_PRIORITY];
>> +       u32 addr;
>> +       u16 len;
>> +       u16 offset;
>> +};
>> +
>> +/**
>> + * rsc_hdr: resource header information
>
>ditto.
>
Will do.

>> + *
>> + * @slv_id: id for the resource
>> + * @header_offset: Entry header offset from data
>> + * @data_offset: Entry offset for data location
>
>Same question: offset from where?
>
Ok

>> + * @cnt: number of entries for HW type
>> + * @version: MSB is major, LSB is minor
>
>@reserved: reserved for future use
>
Ok.
>> + */
>> +struct rsc_hdr {
>> +       u16 slv_id;
>> +       u16 header_offset;
>> +       u16 data_offset;
>> +       u16 cnt;
>> +       u16 version;
>> +       u16 reserved[3];
>> +};
>> +
>> +/**
>> + * cmd_db_header: The DB header information
>> + *
>> + * @version: The cmd db version
>> + * @magic_number: constant expected in the database
>> + * @header: array of resources
>> + * @check_sum: check sum for the header. Unused.
>> + * @reserved: reserved memory
>> + * @data: driver specific data
>> + */
>> +struct cmd_db_header {
>> +       u32 version;
>> +       u32 magic_num;
>> +       struct rsc_hdr header[MAX_SLV_ID];
>> +       u32 check_sum;
>
>Drop underscore? 'checksum' is usually one word.
>
Sure.

>> +       u32 reserved;
>> +       u8 data[];
>> +};
>> +
>> +/**
>> + * DOC: Description of the Command DB database.
>> + *
>> + * At the start of the command DB memory is the cmd_db_header structure.
>> + * The cmd_db_header holds the version, checksum, magic key as well as an
>> + * array for header for each slave (depicted by the rsc_header). Each h/w
>> + * based accelerator is a 'slave' (shared resource) and has slave id indicating
>> + * the type of accelerator. The rsc_header is the header for such individual
>> + * slaves of a given type. The entries for each of these slaves begin at the
>> + * rsc_hdr.header_offset. In addition each slave could have auxiliary data
>> + * that may be needed by the driver. The data for the slave starts at the
>> + * entry_header.offset to the location pointed to by the rsc_hdr.data_offset.
>> + *
>> + * Drivers have a stringified key to a slave/resource. They can query the slave
>> + * information and get the slave id and the auxiliary data and the length of the
>> + * data. Using this information, they can format the request to be sent to the
>> + * h/w accelerator and request a resource state.
>> + */
>> +
>> +static struct cmd_db_header *cmd_db_header;
>> +
>> +/**
>> + * cmd_db_ready - Indicates if command DB is available
>> + *
>> + * Return: 0 on success, errno otherwise
>> + */
>> +int cmd_db_ready(void)
>> +{
>> +       if (cmd_db_header == NULL)
>> +               return -EPROBE_DEFER;
>> +       else if (cmd_db_header->magic_num != CMD_DB_MAGIC)
>> +               return -EINVAL;
>> +       else
>> +               return 0;
>
>Drop else and just return 0.
>
Ok.

>> +}
>> +EXPORT_SYMBOL(cmd_db_ready);
>> +
>> +static u64 cmd_db_get_u64_id(const char *id)
>> +{
>> +       u64 rsc_id = 0;
>> +       u8 *ch = (u8 *)&rsc_id;
>> +       int i;
>> +
>> +       for (i = 0; i < sizeof(rsc_id) && id[i]; i++)
>> +               ch[i] = id[i];
>
>This could be a strncpy now? Didn't I already ask this? I'll have to
>look back at the other emails it seems. Actually, it looks like a cast
>of a string to an integer,
Yes, you did ask. The cast helps do an integer comparison as opposed to
string comparision on the database.

>which is then reversed to look up the same
>string. Not sure what the use is for this.
>
Where do you see that?

>> +
>> +       return rsc_id;
>> +}
>> +
>> +static int cmd_db_get_header(u64 query, struct entry_header *eh,
>> +                           struct rsc_hdr *rh)
>> +{
>> +       struct rsc_hdr *rsc_hdr;
>> +       struct entry_header *ent;
>> +       int ret, i, j;
>> +
>> +       ret = cmd_db_ready();
>> +       if (ret)
>> +               return ret;
>> +
>> +       if (!eh || !rh)
>> +               return -EINVAL;
>> +
>> +       for (i = 0; i < MAX_SLV_ID; i++) {
>> +               rsc_hdr = &cmd_db_header->header[i];
>> +               if (!rsc_hdr->slv_id)
>> +                       break;
>> +
>> +               ent = ENTRY_HEADER(rsc_hdr);
>> +               for (j = 0; j < rsc_hdr->cnt; j++, ent++) {
>> +                       if (ent->id == query)
>> +                               break;
>> +               }
>> +
>> +               if (j < rsc_hdr->cnt) {
>> +                       memcpy(eh, ent, sizeof(*ent));
>> +                       memcpy(rh, rsc_hdr, sizeof(*rh));
>
>I suppose it's OK to punt on the endian issues for now if it's too hard.
>Eventually we'll want to handle it though and it shouldn't make the code
>any worse when endianness is the same. Can it be done now?
>
Why is the change in endian needed? We can always add that in later if
we decide to change the default endian. I would prefer that we punt it
for now.

>> +                       return 0;
>> +               }
>> +       }
>> +
>> +       return -ENODEV;
>> +}
>> +
>> +static int cmd_db_get_header_by_rsc_id(const char *id,
>> +                                     struct entry_header *ent_hdr,
>> +                                     struct rsc_hdr *rsc_hdr)
>> +{
>> +       u64 rsc_id = cmd_db_get_u64_id(id);
>> +
>> +       return cmd_db_get_header(rsc_id, ent_hdr, rsc_hdr);
>> +}
>> +
>> +/**
>> + * cmd_db_read_addr() - Query command db for resource id address.
>> + *
>> + *  @id: resource id to query for address
>> + *
>> + * This is used to retrieve resource address based on resource
>> + * id.
>> + *  Return: resource address on success, 0 on error
>
>Weird spaces here. Mix of tabs and spaces perhaps?
>
Hmm. Not sure, didn't see checkpatch complain. Will check.

>> + */
>> +u32 cmd_db_read_addr(const char *id)
>> +{
>> +       int ret;
>> +       struct entry_header ent;
>> +       struct rsc_hdr rsc_hdr;
>> +
>> +       ret = cmd_db_get_header_by_rsc_id(id, &ent, &rsc_hdr);
>> +
>> +       return ret < 0 ? 0 : ent.addr;
>> +}
>> +EXPORT_SYMBOL(cmd_db_read_addr);
>> +
>> +/**
>> + * cmd_db_read_aux_data() - Query command db for aux data.
>> + *
>> + *  @id : Resource to retrieve AUX Data on.
>> + *  @data : Data buffer to copy returned aux data to. Returns size on NULL
>> + *  @len : Caller provides size of data buffer passed in.
>
>Attach the ':' to the variable please.
>
Ok
>> + *
>> + *  Return: size of data on success, errno on error
>
>success, -EINVAL on error
>
Ok

>> + */
>> +int cmd_db_read_aux_data(const char *id, u8 *data, int len)
>> +{
>> +       int ret;
>> +       struct entry_header ent;
>> +       struct rsc_hdr rsc_hdr;
>> +
>> +       if (!data)
>> +               return -EINVAL;
>> +
>> +       ret = cmd_db_get_header_by_rsc_id(id, &ent, &rsc_hdr);
>> +       if (ret)
>> +               return ret;
>> +
>> +       if (len < ent.len)
>> +               return -EINVAL;
>> +
>> +       len = min_t(u16, ent.len, len);
>> +       memcpy(data, RSC_OFFSET(rsc_hdr, ent), len);
>> +
>> +       return len;
>> +}
>> +EXPORT_SYMBOL(cmd_db_read_aux_data);
>> +
>> +/**
>> + * cmd_db_read_aux_data_len - Get the length of the auxllary data stored in DB.
>> + *
>> + * @id: Resource to retrieve AUX Data.
>> + *
>> + * Return: size on success, 0 on error
>> + */
>> +size_t cmd_db_read_aux_data_len(const char *id)
>> +{
>> +       int ret;
>> +       struct entry_header ent;
>> +       struct rsc_hdr rsc_hdr;
>> +
>> +       ret = cmd_db_get_header_by_rsc_id(id, &ent, &rsc_hdr);
>
>A bunch of code is calling this function. Why not change the user
>interface to use an opaque 'resource' cookie that we can 'get' or 'find'
>and then use that cookie in the rest of the API to pull out the data
>that's desired?
>
Fair point. Let me find out. I suspect this was done to keep the API
similar to other non-Linux interfaces. I am not sure why they all didn't
use a handle instead of char *.

>> +
>> +       return ret < 0 ? 0 : ent.len;
>> +}
>> +EXPORT_SYMBOL(cmd_db_read_aux_data_len);
>> +
>> +/**
>> + * cmd_db_read_slave_id - Get the slave ID for a given resource address
>> + *
>> + * @id: Resource id to query the DB for version
>> + *
>> + * Return: cmd_db_hw_type enum on success, CMD_DB_HW_INVALID on error
>> + */
>> +enum cmd_db_hw_type cmd_db_read_slave_id(const char *id)
>> +{
>> +       int ret;
>> +       struct entry_header ent;
>> +       struct rsc_hdr rsc_hdr;
>> +
>> +       ret = cmd_db_get_header_by_rsc_id(id, &ent, &rsc_hdr);
>> +
>> +       return ret < 0 ? CMD_DB_HW_INVALID :
>> +                      (ent.addr >> SLAVE_ID_SHIFT) & SLAVE_ID_MASK;
>> +}
>> +EXPORT_SYMBOL(cmd_db_read_slave_id);
>> +
>> +static int cmd_db_dev_probe(struct platform_device *pdev)
>> +{
>> +       struct reserved_mem *rmem;
>> +       void *dict, *start_addr;
>> +       int ret = 0;
>> +
>> +       rmem = of_reserved_mem_lookup(pdev->dev.of_node);
>> +       if (!rmem) {
>> +               dev_err(&pdev->dev, "failed to acquire memory region\n");
>> +               return -EINVAL;
>> +       }
>> +
>> +       dict = devm_memremap(&pdev->dev, rmem->base, rmem->size, MEMREMAP_WB);
>> +       if (IS_ERR(dict))
>> +               return -ENOMEM;
>> +
>> +       start_addr = memremap(readl_relaxed(dict), readl_relaxed(dict + 0x4),
>> +                            MEMREMAP_WB);
>> +       if (IS_ERR_OR_NULL(start_addr)) {
>
>Should just be !start_addr? I don't see where memremap() returns an
>error pointer.
>
Sure.

>> +               ret = PTR_ERR(start_addr);
>> +               goto done;
>> +       }
>> +
>> +       cmd_db_header = start_addr;
>> +       if (cmd_db_header->magic_num != CMD_DB_MAGIC) {
>
>memcmp?
>
Why? It could be a simple comparison.

>> +               ret = -EINVAL;
>> +               dev_err(&pdev->dev, "Invalid Command DB Magic\n");
>> +               goto done;
>> +       }
>> +
>> +done:
>> +       devm_memunmap(&pdev->dev, dict);
>
>I'm lost why we use devm_*() for this mapping.
>
Must have picked it up from an example. Curious, why not though?

>> +       return ret;
>> +}
>> +
>> +static const struct of_device_id cmd_db_match_table[] = {
>> +       { .compatible = "qcom,cmd-db" },
>> +       { },
>> +};
>> +
>> +static struct platform_driver cmd_db_dev_driver = {
>> +       .probe  = cmd_db_dev_probe,
>> +       .driver = {
>> +                 .name = "cmd-db",
>> +                 .of_match_table = cmd_db_match_table,
>
>Add suppress_bind_attrs here to make sure we can't remove this device
>later? That also allows us to ignore unmapping the start_addr pointer
>in any sort of 'remove' function.
>
Ok..

Thanks Stephen.

-- Lina

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