linux-kernel - Re: [PATCH 5/8] drm/bridge: it66121: Add a helper function to read chip id

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Message-ID: <7602cd83-0e05-4e11-9bd1-10eb1d48a507@linux.dev>
Date:   Thu, 16 Nov 2023 20:18:12 +0800
From:   Sui Jingfeng <sui.jingfeng@...ux.dev>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     Phong LE <ple@...libre.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Maxime Ripard <mripard@...nel.org>,
        Sui Jingfeng <suijingfeng@...ngson.cn>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Thomas Zimmermann <tzimmermann@...e.de>
Subject: Re: [PATCH 5/8] drm/bridge: it66121: Add a helper function to read
 chip id

Hi,


On 2023/11/15 00:06, Dmitry Baryshkov wrote:
> On Tue, 14 Nov 2023 at 17:09, Sui Jingfeng <sui.jingfeng@...ux.dev> wrote:
>> From: Sui Jingfeng <suijingfeng@...ngson.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@...ngson.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.


Since it6610 was introduced, this is used for chip identifying.
It can also be used with in debugfs context, to show who I am.


>>                  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
>>
>