linux-kernel - Re: [PATCH v2 11/26] drm/rockchip: dw-mipi-dsi: don't assume buffer is aligned

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Message-ID: <58846A70.5040503@rock-chips.com>
Date:   Sun, 22 Jan 2017 16:16:48 +0800
From:   Chris Zhong <zyw@...k-chips.com>
To:     John Keeping <john@...anate.com>,
        Mark Yao <mark.yao@...k-chips.com>
Cc:     dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 11/26] drm/rockchip: dw-mipi-dsi: don't assume buffer
 is aligned

Hi John

Reviewed-by: Chris Zhong <zyw@...k-chips.com>


On 01/22/2017 12:31 AM, John Keeping wrote:
> By dereferencing the MIPI command buffer as a u32* we rely on it being
> correctly aligned on ARM, but this may not be the case.  Copy it into a
> stack variable that will be correctly aligned.
>
> Signed-off-by: John Keeping <john@...anate.com>
> ---
> Unchanged in v2
> ---
>   drivers/gpu/drm/rockchip/dw-mipi-dsi.c | 12 +++++++-----
>   1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/rockchip/dw-mipi-dsi.c b/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
> index 03fc096fe1bd..ddbc037e7ced 100644
> --- a/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
> +++ b/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
> @@ -607,10 +607,10 @@ static int dw_mipi_dsi_dcs_short_write(struct dw_mipi_dsi *dsi,
>   static int dw_mipi_dsi_dcs_long_write(struct dw_mipi_dsi *dsi,
>   				      const struct mipi_dsi_msg *msg)
>   {
> -	const u32 *tx_buf = msg->tx_buf;
> -	int len = msg->tx_len, pld_data_bytes = sizeof(*tx_buf), ret;
> +	const u8 *tx_buf = msg->tx_buf;
> +	int len = msg->tx_len, pld_data_bytes = sizeof(u32), ret;
>   	u32 hdr_val = GEN_HDATA(msg->tx_len) | GEN_HTYPE(msg->type);
> -	u32 remainder = 0;
> +	u32 remainder;
>   	u32 val;
>   
>   	if (msg->tx_len < 3) {
> @@ -621,12 +621,14 @@ static int dw_mipi_dsi_dcs_long_write(struct dw_mipi_dsi *dsi,
>   
>   	while (DIV_ROUND_UP(len, pld_data_bytes)) {
>   		if (len < pld_data_bytes) {
> +			remainder = 0;
>   			memcpy(&remainder, tx_buf, len);
>   			dsi_write(dsi, DSI_GEN_PLD_DATA, remainder);
>   			len = 0;
>   		} else {
> -			dsi_write(dsi, DSI_GEN_PLD_DATA, *tx_buf);
> -			tx_buf++;
> +			memcpy(&remainder, tx_buf, pld_data_bytes);
> +			dsi_write(dsi, DSI_GEN_PLD_DATA, remainder);
> +			tx_buf += pld_data_bytes;
>   			len -= pld_data_bytes;
>   		}
>