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Date:   Fri, 22 Mar 2019 12:51:31 +0200
From:   Tomi Valkeinen <tomi.valkeinen@...com>
To:     Andrey Smirnov <andrew.smirnov@...il.com>,
        <dri-devel@...ts.freedesktop.org>
CC:     Archit Taneja <architt@...eaurora.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Andrey Gusakov <andrey.gusakov@...entembedded.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Chris Healy <cphealy@...il.com>,
        Lucas Stach <l.stach@...gutronix.de>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 07/15] drm/bridge: tc358767: Simplify AUX data write

On 22/03/2019 05:28, Andrey Smirnov wrote:
> Simplify AUX data write by dropping index arithmetic and shifting and
> replacing it with a call to a helper function that does three things:
> 
>     1. Copies user-provided data into a write buffer
>     2. Optionally fixes the endianness of the write buffer (not needed
>        on LE hosts)
>     3. Transfers contenst of the write buffer to up to 4 32-bit
>        registers on the chip
> 
> Note that separate data endianness fix:
> 
>     tmp = (tmp << 8) | buf[i];
> 
> that was reserved for DP_AUX_I2C_WRITE looks really strange, since it
> will place data differently depending on the passed user-data
> size. E.g. for a write of 1 byte, data transferred to the chip would
> look like:
> 
> [byte0] [dummy1] [dummy2] [dummy3]
> 
> whereas for a write of 4 bytes we'd get:
> 
> [byte3] [byte2] [byte1] [byte0]
> 
> Since there's no indication in the datasheet that I2C write buffer
> should be treated differently than AUX write buffer and no comment in
> the original code explaining why it was done this way, that special
> I2C write buffer transformation was dropped in this patch.
> 
> Signed-off-by: Andrey Smirnov <andrew.smirnov@...il.com>
> Cc: Archit Taneja <architt@...eaurora.org>
> 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: 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 | 58 +++++++++++++++++++------------
>  1 file changed, 36 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/tc358767.c b/drivers/gpu/drm/bridge/tc358767.c
> index 81c10a5d8106..21374565585d 100644
> --- a/drivers/gpu/drm/bridge/tc358767.c
> +++ b/drivers/gpu/drm/bridge/tc358767.c
> @@ -307,6 +307,31 @@ static int tc_aux_get_status(struct tc_data *tc, u8 *reply)
>  	return 0;
>  }
>  
> +static int tc_aux_write_data(struct tc_data *tc, const void *data,
> +			     size_t size)
> +{
> +	u32 auxwdata[DP_AUX_MAX_PAYLOAD_BYTES / sizeof(u32)] = { 0 };
> +	int ret, i, count = DIV_ROUND_UP(size, 4);

Should 4 there be sizeof(u32)?

> +
> +	memcpy(auxwdata, data, size);
> +
> +	for (i = 0; i < count; i++) {
> +		ret = regmap_write(tc->regmap, DP0_AUXWDATA(i),
> +				   /*
> +				    * Our regmap is configured as LE
> +				    * for register data, so we need
> +				    * undo any byte swapping that will
> +				    * happened to preserve original
> +				    * byte order.
> +				    */
> +				   cpu_to_le32(auxwdata[i]));

Can regmap_bulk_write or regmap_raw_write be used here?

 Tomi

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