linux-kernel - Re: [PATCH v4 10/15] drm/bridge: tc358767: Add support for address-only I2C transfers

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Date:   Fri, 7 Jun 2019 08:13:24 +0200
From:   Andrzej Hajda <a.hajda@...sung.com>
To:     Andrey Smirnov <andrew.smirnov@...il.com>,
        dri-devel@...ts.freedesktop.org
Cc:     Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Andrey Gusakov <andrey.gusakov@...entembedded.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Cory Tusar <cory.tusar@....aero>,
        Chris Healy <cphealy@...il.com>,
        Lucas Stach <l.stach@...gutronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 10/15] drm/bridge: tc358767: Add support for
 address-only I2C transfers

On 07.06.2019 06:45, Andrey Smirnov wrote:
> Transfer size of zero means a request to do an address-only
> transfer. Since the HW support this, we probably shouldn't be just
> ignoring such requests. While at it allow DP_AUX_I2C_MOT flag to pass
> through, since it is supported by the HW as well.
>
> Signed-off-by: Andrey Smirnov <andrew.smirnov@...il.com>
Reviewed-by: Andrzej Hajda <a.hajda@...sung.com>

 --
Regards
Andrzej
> Cc: Andrzej Hajda <a.hajda@...sung.com>
> Cc: Laurent Pinchart <Laurent.pinchart@...asonboard.com>
> Cc: Tomi Valkeinen <tomi.valkeinen@...com>
> Cc: Andrey Gusakov <andrey.gusakov@...entembedded.com>
> Cc: Philipp Zabel <p.zabel@...gutronix.de>
> Cc: Cory Tusar <cory.tusar@....aero>
> Cc: Chris Healy <cphealy@...il.com>
> Cc: Lucas Stach <l.stach@...gutronix.de>
> Cc: dri-devel@...ts.freedesktop.org
> Cc: linux-kernel@...r.kernel.org
> ---
>  drivers/gpu/drm/bridge/tc358767.c | 30 +++++++++++++++++++++++-------
>  1 file changed, 23 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/tc358767.c b/drivers/gpu/drm/bridge/tc358767.c
> index 7d0fbb12195b..4bb9b15e1324 100644
> --- a/drivers/gpu/drm/bridge/tc358767.c
> +++ b/drivers/gpu/drm/bridge/tc358767.c
> @@ -145,6 +145,8 @@
>  
>  /* AUX channel */
>  #define DP0_AUXCFG0		0x0660
> +#define DP0_AUXCFG0_BSIZE	GENMASK(11, 8)
> +#define DP0_AUXCFG0_ADDR_ONLY	BIT(4)
>  #define DP0_AUXCFG1		0x0664
>  #define AUX_RX_FILTER_EN		BIT(16)
>  
> @@ -327,6 +329,18 @@ static int tc_aux_read_data(struct tc_data *tc, void *data, size_t size)
>  	return size;
>  }
>  
> +static u32 tc_auxcfg0(struct drm_dp_aux_msg *msg, size_t size)
> +{
> +	u32 auxcfg0 = msg->request;
> +
> +	if (size)
> +		auxcfg0 |= FIELD_PREP(DP0_AUXCFG0_BSIZE, size - 1);
> +	else
> +		auxcfg0 |= DP0_AUXCFG0_ADDR_ONLY;
> +
> +	return auxcfg0;
> +}
> +
>  static ssize_t tc_aux_transfer(struct drm_dp_aux *aux,
>  			       struct drm_dp_aux_msg *msg)
>  {
> @@ -336,9 +350,6 @@ static ssize_t tc_aux_transfer(struct drm_dp_aux *aux,
>  	u32 auxstatus;
>  	int ret;
>  
> -	if (size == 0)
> -		return 0;
> -
>  	ret = tc_aux_wait_busy(tc, 100);
>  	if (ret)
>  		return ret;
> @@ -362,8 +373,7 @@ static ssize_t tc_aux_transfer(struct drm_dp_aux *aux,
>  	if (ret)
>  		return ret;
>  	/* Start transfer */
> -	ret = regmap_write(tc->regmap, DP0_AUXCFG0,
> -			   ((size - 1) << 8) | request);
> +	ret = regmap_write(tc->regmap, DP0_AUXCFG0, tc_auxcfg0(msg, size));
>  	if (ret)
>  		return ret;
>  
> @@ -377,8 +387,14 @@ static ssize_t tc_aux_transfer(struct drm_dp_aux *aux,
>  
>  	if (auxstatus & AUX_TIMEOUT)
>  		return -ETIMEDOUT;
> -
> -	size = FIELD_GET(AUX_BYTES, auxstatus);
> +	/*
> +	 * For some reason address-only DP_AUX_I2C_WRITE (MOT), still
> +	 * reports 1 byte transferred in its status. To deal we that
> +	 * we ignore aux_bytes field if we know that this was an
> +	 * address-only transfer
> +	 */
> +	if (size)
> +		size = FIELD_GET(AUX_BYTES, auxstatus);
>  	msg->reply = FIELD_GET(AUX_STATUS, auxstatus);
>  
>  	switch (request) {