[PATCH v4 1/1] drm/bridge: it6505: fix hibernate to resume no display issue

[Pin-yen Lin]

Hi Kuro,

On Fri, Mar 8, 2024 at 4:54 PM kuro <kuro.chung at ite.com.tw> wrote:
>
> From: Kuro <kuro.chung at ite.com.tw>
>
> ITE added a FIFO reset bit for input video. When system power resume,
> the TTL input of it6505 may get some noise before video signal stable
> and the hardware function reset is required.
> But the input FIFO reset will also trigger error interrupts of output module rising.
> Thus, it6505 have to wait a period can clear those expected error interrupts
> caused by manual hardware reset in one interrupt handler calling to avoid interrupt looping.
>
> Signed-off-by: Kuro Chung <kuro.chung at ite.corp-partner.google.com>
>
> ---
>  drivers/gpu/drm/bridge/ite-it6505.c | 50 ++++++++++++++++++++---------
>  1 file changed, 35 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/ite-it6505.c b/drivers/gpu/drm/bridge/ite-it6505.c
> index b53da9bb65a16..eff888fe7c2e7 100644
> --- a/drivers/gpu/drm/bridge/ite-it6505.c
> +++ b/drivers/gpu/drm/bridge/ite-it6505.c
> @@ -1318,6 +1318,8 @@ static void it6505_video_reset(struct it6505 *it6505)
>         it6505_set_bits(it6505, REG_DATA_MUTE_CTRL, EN_VID_MUTE, EN_VID_MUTE);
>         it6505_set_bits(it6505, REG_INFOFRAME_CTRL, EN_VID_CTRL_PKT, 0x00);
>         it6505_set_bits(it6505, REG_RESET_CTRL, VIDEO_RESET, VIDEO_RESET);
> +       it6505_set_bits(it6505, REG_VID_BUS_CTRL1, TX_FIFO_RESET, 0x02);
> +       it6505_set_bits(it6505, REG_VID_BUS_CTRL1, TX_FIFO_RESET, 0x00);
>         it6505_set_bits(it6505, REG_501_FIFO_CTRL, RST_501_FIFO, RST_501_FIFO);
>         it6505_set_bits(it6505, REG_501_FIFO_CTRL, RST_501_FIFO, 0x00);
>         it6505_set_bits(it6505, REG_RESET_CTRL, VIDEO_RESET, 0x00);
> @@ -2475,31 +2477,49 @@ static void it6505_irq_link_train_fail(struct it6505 *it6505)
>         schedule_work(&it6505->link_works);
>  }
>
> -static void it6505_irq_video_fifo_error(struct it6505 *it6505)
> +static bool it6505_test_bit(unsigned int bit, const unsigned int *addr)
>  {
> -       struct device *dev = &it6505->client->dev;
> +       return 1 & (addr[bit / BITS_PER_BYTE] >> (bit % BITS_PER_BYTE));
> +}
>
> -       DRM_DEV_DEBUG_DRIVER(dev, "video fifo overflow interrupt");
> -       it6505->auto_train_retry = AUTO_TRAIN_RETRY;
> -       flush_work(&it6505->link_works);
> -       it6505_stop_hdcp(it6505);
> -       it6505_video_reset(it6505);
> +static bool it6505_is_video_error_int(const int *int_status)
> +{
> +       if ((it6505_test_bit(BIT_INT_VID_FIFO_ERROR, (unsigned int *)int_status)) || (it6505_test_bit(BIT_INT_IO_FIFO_OVERFLOW, (unsigned int *)int_status)))
> +               return 1;
> +       return 0;
>  }
>
> -static void it6505_irq_io_latch_fifo_overflow(struct it6505 *it6505)
> +static void it6505_irq_video_error_handler(struct it6505 *it6505)
>  {
>         struct device *dev = &it6505->client->dev;
> +       int int_status[3] = {0};
> +       int reg_0d;
> +       int i;
>
> -       DRM_DEV_DEBUG_DRIVER(dev, "IO latch fifo overflow interrupt");
>         it6505->auto_train_retry = AUTO_TRAIN_RETRY;
>         flush_work(&it6505->link_works);
>         it6505_stop_hdcp(it6505);
>         it6505_video_reset(it6505);
> -}
>
> -static bool it6505_test_bit(unsigned int bit, const unsigned int *addr)
> -{
> -       return 1 & (addr[bit / BITS_PER_BYTE] >> (bit % BITS_PER_BYTE));
> +       DRM_DEV_DEBUG_DRIVER(dev, "Video Error reset wait video...");
> +

I still don't see any code comment around the following section.

> +       for (i = 0; i < 10; i++) {
> +               usleep_range(10000, 11000);
> +               int_status[2] = it6505_read(it6505, INT_STATUS_03);
> +               reg_0d = it6505_read(it6505, REG_SYSTEM_STS);
> +               it6505_write(it6505, INT_STATUS_03, int_status[2]);
> +
> +               DRM_DEV_DEBUG_DRIVER(dev, "reg08 = 0x%02x", int_status[2]);
> +               DRM_DEV_DEBUG_DRIVER(dev, "reg0D = 0x%02x", reg_0d);
> +
> +               if ((reg_0d & VIDEO_STB) && (reg_0d >= 0))
> +                       break;
> +
> +               if (it6505_is_video_error_int(int_status)) {
> +                       it6505_video_reset(it6505);
> +                       DRM_DEV_DEBUG_DRIVER(dev, "Video Error reset wait video (%d)", i);
> +               }
> +       }

Okay let me make the questions more specific:

1. What would happen if we remove the loop and only check the video
error interrupts once? If another video error interrupt comes out, we
handle it in the next interrupt handler. Will this lead to an infinite
loop?

2. Why do we run the loop for 10 times (100ms as you mentioned), but
not 5 times or 20 times? Does this "100ms" come from the hardware spec
or your experience on debugging this issue? I guess it's okay if it's
"I tried it a few times and 100ms seems to be just enough", but I
would prefer you to write that down in the code comments.

>  }
>
>  static irqreturn_t it6505_int_threaded_handler(int unused, void *data)
> @@ -2519,8 +2539,6 @@ static irqreturn_t it6505_int_threaded_handler(int unused, void *data)
>                 { BIT_INT_HDCP_KSV_CHECK, it6505_irq_hdcp_ksv_check },
>                 { BIT_INT_AUDIO_FIFO_ERROR, it6505_irq_audio_fifo_error },
>                 { BIT_INT_LINK_TRAIN_FAIL, it6505_irq_link_train_fail },
> -               { BIT_INT_VID_FIFO_ERROR, it6505_irq_video_fifo_error },
> -               { BIT_INT_IO_FIFO_OVERFLOW, it6505_irq_io_latch_fifo_overflow },
>         };
>         int int_status[3], i;
>
> @@ -2550,6 +2568,8 @@ static irqreturn_t it6505_int_threaded_handler(int unused, void *data)
>                         if (it6505_test_bit(irq_vec[i].bit, (unsigned int *)int_status))
>                                 irq_vec[i].handler(it6505);
>                 }
> +               if (it6505_is_video_error_int(int_status))
> +                       it6505_irq_video_error_handler(it6505);
>         }
>
>         pm_runtime_put_sync(dev);
> --
> 2.25.1
>

Regards,
Pin-yen