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Message-ID: <2a9fda42-0c7a-420b-81cc-653861a3dcd8@linux.dev>
Date:   Thu, 23 Nov 2023 21:03:48 +0800
MIME-Version: 1.0
Subject: Re: [PATCH 5/8] drm/bridge: it66121: Add a helper function to read
 chip id
To:     Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Cc:     Phong LE <ple@baylibre.com>,
        Neil Armstrong <neil.armstrong@linaro.org>,
        Maxime Ripard <mripard@kernel.org>,
        Sui Jingfeng <suijingfeng@loongson.cn>,
        linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
        Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        Thomas Zimmermann <tzimmermann@suse.de>
References: <20231114150130.497915-1-sui.jingfeng@linux.dev>
 <20231114150130.497915-6-sui.jingfeng@linux.dev>
 <CAA8EJprkDpjuHEi5R01p4XNvFBr94BvXhr7AZCLr6dC8Mk=yPw@mail.gmail.com>
 <7602cd83-0e05-4e11-9bd1-10eb1d48a507@linux.dev>
 <CAA8EJprFjdrQtegJd5HyzGYQaMawwQOhvkE=SNqsdsBCrtfDTA@mail.gmail.com>
 <14f859f2-6661-4955-932b-1ae22ae134fe@linux.dev>
 <CAA8EJppnB-FbnS20eJg1jwKP7pQwV_etYkQg2YW75SEO8kF9MA@mail.gmail.com>
Content-Language: en-US
From:   Sui Jingfeng <sui.jingfeng@linux.dev>
In-Reply-To: <CAA8EJppnB-FbnS20eJg1jwKP7pQwV_etYkQg2YW75SEO8kF9MA@mail.gmail.com>
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Hi,


On 2023/11/23 15:48, Dmitry Baryshkov wrote:
> On Thu, 23 Nov 2023 at 07:37, Sui Jingfeng <sui.jingfeng@linux.dev> wrote:
>> Hi,
>>
>>
>> On 2023/11/16 21:00, Dmitry Baryshkov wrote:
>>> On Thu, 16 Nov 2023 at 14:18, Sui Jingfeng <sui.jingfeng@linux.dev> wrote:
>>>> Hi,
>>>>
>>>>
>>>> On 2023/11/15 00:06, Dmitry Baryshkov wrote:
>>>>> On Tue, 14 Nov 2023 at 17:09, Sui Jingfeng <sui.jingfeng@linux.dev> wrote:
>>>>>> From: Sui Jingfeng <suijingfeng@loongson.cn>
>>>>>>
>>>>>> Read the required chip id data back by calling regmap_bulk_read() once,
>>>>>> reduce the number of local variables needed in it66121_probe() function.
>>>>>> And store its values into struct it66121_ctx, as it will be used latter.
>>>>>>
>>>>>> Signed-off-by: Sui Jingfeng <suijingfeng@loongson.cn>
>>>>>> ---
>>>>>>     drivers/gpu/drm/bridge/ite-it66121.c | 47 ++++++++++++++++++++--------
>>>>>>     1 file changed, 34 insertions(+), 13 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/gpu/drm/bridge/ite-it66121.c b/drivers/gpu/drm/bridge/ite-it66121.c
>>>>>> index 7e473beefc79..f36d05331f25 100644
>>>>>> --- a/drivers/gpu/drm/bridge/ite-it66121.c
>>>>>> +++ b/drivers/gpu/drm/bridge/ite-it66121.c
>>>>>> @@ -313,6 +313,9 @@ struct it66121_ctx {
>>>>>>                    bool auto_cts;
>>>>>>            } audio;
>>>>>>            const struct it66121_chip_info *info;
>>>>>> +       u16 vender_id;
>>>>>> +       u16 device_id;
>>>>>> +       u8 revision;
>>>>> There is no need to store them, they are not used by the driver anywhere.
>>>>>
>>>>>>     };
>>>>>>
>>>>>>     static inline struct it66121_ctx *bridge_to_it66121(struct drm_bridge *bridge)
>>>>>> @@ -399,6 +402,30 @@ static void it66121_hw_reset(struct it66121_ctx *ctx)
>>>>>>            gpiod_set_value(ctx->gpio_reset, 0);
>>>>>>     }
>>>>>>
>>>>>> +static int it66121_read_chip_id(struct it66121_ctx *ctx, bool verbose)
>>>>>> +{
>>>>>> +       u8 id[4];
>>>>>> +       int ret;
>>>>>> +
>>>>>> +       ret = regmap_bulk_read(ctx->regmap, IT66121_VENDOR_ID0_REG, id, 4);
>>>>>> +       if (ret < 0) {
>>>>>> +               dev_err(ctx->dev, "Failed to read chip ID: %d\n", ret);
>>>>>> +               return ret;
>>>>>> +       }
>>>>>> +
>>>>>> +       ctx->vender_id = (u16)id[1] << 8 | id[0];
>>>>>> +       ctx->device_id = ((u16)(id[3] & IT66121_DEVICE_ID1_MASK) << 8 | id[2]);
>>>>>> +       /* Revision is shared with DEVICE_ID1 */
>>>>>> +       ctx->revision = FIELD_GET(IT66121_REVISION_MASK, id[3]);
>>>>>> +
>>>>>> +       if (verbose) {
>>>>>> +               dev_info(ctx->dev, "Found ITE66121: 0x%x%x, revision: %u\n",
>>>>>> +                        ctx->vender_id, ctx->device_id, ctx->revision);
>>>>>> +       }
>>>>>> +
>>>>>> +       return 0;
>>>>>> +}
>>>>>> +
>>>>>>     static inline int it66121_preamble_ddc(struct it66121_ctx *ctx)
>>>>>>     {
>>>>>>            return regmap_write(ctx->regmap, IT66121_MASTER_SEL_REG, IT66121_MASTER_SEL_HOST);
>>>>>> @@ -1561,7 +1588,6 @@ static const char * const it66121_supplies[] = {
>>>>>>
>>>>>>     static int it66121_probe(struct i2c_client *client)
>>>>>>     {
>>>>>> -       u32 revision_id, vendor_ids[2] = { 0 }, device_ids[2] = { 0 };
>>>>>>            int ret;
>>>>>>            struct it66121_ctx *ctx;
>>>>>>            struct device *dev = &client->dev;
>>>>>> @@ -1603,19 +1629,13 @@ static int it66121_probe(struct i2c_client *client)
>>>>>>            if (IS_ERR(ctx->regmap))
>>>>>>                    return PTR_ERR(ctx->regmap);
>>>>>>
>>>>>> -       regmap_read(ctx->regmap, IT66121_VENDOR_ID0_REG, &vendor_ids[0]);
>>>>>> -       regmap_read(ctx->regmap, IT66121_VENDOR_ID1_REG, &vendor_ids[1]);
>>>>>> -       regmap_read(ctx->regmap, IT66121_DEVICE_ID0_REG, &device_ids[0]);
>>>>>> -       regmap_read(ctx->regmap, IT66121_DEVICE_ID1_REG, &device_ids[1]);
>>>>>> -
>>>>>> -       /* Revision is shared with DEVICE_ID1 */
>>>>>> -       revision_id = FIELD_GET(IT66121_REVISION_MASK, device_ids[1]);
>>>>>> -       device_ids[1] &= IT66121_DEVICE_ID1_MASK;
>>>>>> +       ret = it66121_read_chip_id(ctx, false);
>>>>>> +       if (ret)
>>>>>> +               return ret;
>>>>>>
>>>>>> -       if ((vendor_ids[1] << 8 | vendor_ids[0]) != ctx->info->vid ||
>>>>>> -           (device_ids[1] << 8 | device_ids[0]) != ctx->info->pid) {
>>>>>> +       if (ctx->vender_id != ctx->info->vid ||
>>>>>> +           ctx->device_id != ctx->info->pid)
>>>> Q: There is no need to store them, they are not used by the driver anywhere.
>>>>
>>>> A: Here it is used, it is also used by the 0007-patch to get the entity(instance)-specific data.
>>> And the patch 7 will be changed once you have proper i2c client struct
>>> registered.
>>>
>>>> Since it6610 was introduced, this is used for chip identifying.
>>>> It can also be used with in debugfs context, to show who I am.
>>> I'd say, there is little point in whoami debugfs files. Debugfs is for
>>> the useful information.
>> Sinceit6610 was introduced, how do you know what the device it66121 driver is
>> binding? Printing model specific information is common practice for a
>> large driver. Especially if you can only able to debug remotely where
>> only a SSH is given.
> cat /sys/bus/i2c/devices/.../name

No, this is not enough. This is also not straight-forward.
Because the system will have multiple i2c device. This is
a bit hard to find which one is corresponding to the it66121.

This is needed during the development and debug phase.
We will also want to know the vendor id, device id and revision id.
As those chip id are constant values, matching those chip id against
the values in datasheet is a kind of sanity test. Which helps us to
know if the i2c regmap(the communication channel) has been setup
successfully or not.


>> You could see debugfs of drm/etnaviv for a
>> reference. It is common to testing a large driver running on 20+
>> machines with various hardware model.
>>
>>
>>>>>>                    return -ENODEV;
>>>>>> -       }
>>>>>>
>>>>>>            ctx->bridge.funcs = &it66121_bridge_funcs;
>>>>>>            ctx->bridge.of_node = dev->of_node;
>>>>>> @@ -1633,7 +1653,8 @@ static int it66121_probe(struct i2c_client *client)
>>>>>>
>>>>>>            drm_bridge_add(&ctx->bridge);
>>>>>>
>>>>>> -       dev_info(dev, "IT66121 revision %d probed\n", revision_id);
>>>>>> +       dev_info(dev, "IT66121 probed, chip id: 0x%x:0x%x, revision: %u\n",
>>>>>> +                ctx->vender_id, ctx->device_id, ctx->revision);
>>>>>>
>>>>>>            return 0;
>>>>>>     }
>>>>>> --
>>>>>> 2.34.1
>>>>>>
>>>
>
>