linux-kernel - Re: [PATCH v2 09/18] media: i2c: max9271: Introduce wake

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Message-ID: <YE/VBi3uXPP48nPr@pendragon.ideasonboard.com>
Date:   Mon, 15 Mar 2021 23:43:34 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Jacopo Mondi <jacopo+renesas@...ndi.org>
Cc:     kieran.bingham+renesas@...asonboard.com,
        niklas.soderlund+renesas@...natech.se, geert@...ux-m68k.org,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 09/18] media: i2c: max9271: Introduce wake_up()
 function

Hi Jacopo,

Thank you for the patch.

On Mon, Mar 15, 2021 at 02:15:03PM +0100, Jacopo Mondi wrote:
> The MAX9271 chip manual prescribes a delay of 5 milliseconds
> after the chip exists from low power state.

I don't think we'll ever try to access the chip within 5ms of the
beginning of its existence.

s/exists/exits/

:-)

> Add a new function to the max9271 library driver that wakes up the chip
> with a dummy i2c transaction and implements the correct delay of 5
> milliseconds after the chip exits from low power state.
> 
> Use the newly introduced function in the rdacm20 and rdacm21 camera
> drivers. The former was not respecting the required delay while the
> latter was waiting for a too-short timeout.
> 
> Do not handle the initial i2c address configuration in the library
> driver function as the camera module drivers control address
> reprogramming.

Isn't the initial address fixed though ? Nonetheless, this can be
addressed separately, so

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

> Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
> ---
>  drivers/media/i2c/max9271.c | 7 +++++++
>  drivers/media/i2c/max9271.h | 9 +++++++++
>  drivers/media/i2c/rdacm20.c | 2 +-
>  drivers/media/i2c/rdacm21.c | 3 +--
>  4 files changed, 18 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/media/i2c/max9271.c b/drivers/media/i2c/max9271.c
> index 2c7dc7fb9846..f7bfe7266763 100644
> --- a/drivers/media/i2c/max9271.c
> +++ b/drivers/media/i2c/max9271.c
> @@ -80,6 +80,13 @@ static int max9271_pclk_detect(struct max9271_device *dev)
>  	return -EIO;
>  }
>  
> +void max9271_wake_up(struct max9271_device *dev)
> +{
> +	i2c_smbus_read_byte(dev->client);
> +	usleep_range(5000, 8000);
> +}
> +EXPORT_SYMBOL_GPL(max9271_wake_up);
> +
>  int max9271_set_serial_link(struct max9271_device *dev, bool enable)
>  {
>  	int ret;
> diff --git a/drivers/media/i2c/max9271.h b/drivers/media/i2c/max9271.h
> index d78fb21441e9..dc5e4e70ba6f 100644
> --- a/drivers/media/i2c/max9271.h
> +++ b/drivers/media/i2c/max9271.h
> @@ -85,6 +85,15 @@ struct max9271_device {
>  	struct i2c_client *client;
>  };
>  
> +/**
> + * max9271_wake_up() - Wake up the serializer by issuing an i2c transaction
> + * @dev: The max9271 device
> + *
> + * This function shall be called before any other interaction with the
> + * serializer.
> + */
> +void max9271_wake_up(struct max9271_device *dev);
> +
>  /**
>   * max9271_set_serial_link() - Enable/disable serial link
>   * @dev: The max9271 device
> diff --git a/drivers/media/i2c/rdacm20.c b/drivers/media/i2c/rdacm20.c
> index b9aaa0f7db42..2265ef7c65d4 100644
> --- a/drivers/media/i2c/rdacm20.c
> +++ b/drivers/media/i2c/rdacm20.c
> @@ -459,7 +459,7 @@ static int rdacm20_initialize(struct rdacm20_device *dev)
>  
>  	/* Verify communication with the MAX9271: ping to wakeup. */
>  	dev->serializer.client->addr = MAX9271_DEFAULT_ADDR;
> -	i2c_smbus_read_byte(dev->serializer.client);
> +	max9271_wake_up(&dev->serializer);
>  
>  	/* Serial link disabled during config as it needs a valid pixel clock. */
>  	ret = max9271_set_serial_link(&dev->serializer, false);
> diff --git a/drivers/media/i2c/rdacm21.c b/drivers/media/i2c/rdacm21.c
> index 179d107f494c..7bce55adfd7c 100644
> --- a/drivers/media/i2c/rdacm21.c
> +++ b/drivers/media/i2c/rdacm21.c
> @@ -452,8 +452,7 @@ static int rdacm21_initialize(struct rdacm21_device *dev)
>  
>  	/* Verify communication with the MAX9271: ping to wakeup. */
>  	dev->serializer.client->addr = MAX9271_DEFAULT_ADDR;
> -	i2c_smbus_read_byte(dev->serializer.client);
> -	usleep_range(3000, 5000);
> +	max9271_wake_up(&dev->serializer);
>  
>  	/* Enable reverse channel and disable the serial link. */
>  	ret = max9271_set_serial_link(&dev->serializer, false);

-- 
Regards,

Laurent Pinchart