linux-kernel - Re: [PATCH v3 10/24] drm/rockchip: dw-mipi-dsi: don't assume buffer is aligned

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Date:   Mon, 30 Jan 2017 15:08:11 -0500
From:   Sean Paul <seanpaul@...omium.org>
To:     John Keeping <john@...anate.com>
Cc:     Mark Yao <mark.yao@...k-chips.com>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        linux-rockchip@...ts.infradead.org,
        Chris Zhong <zyw@...k-chips.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 10/24] drm/rockchip: dw-mipi-dsi: don't assume buffer
 is aligned

On Sun, Jan 29, 2017 at 01:24:30PM +0000, 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>
> Reviewed-by: Chris Zhong <zyw@...k-chips.com>
> ---
> v3:
> - Add Chris' Reviewed-by
> 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;
>  		}

You can clean this up further by removing a couple of the locals, the
conditional and the division:

while(len < msg->tx_len) {
        size_t to_write = MIN(msg->tx_len - len, sizeof(remainder));

        memcpy(&remainder, msg->tx_buf + len, to_write);
        dsi_write(dsi, DSI_GEN_PLD_DATA, remainder);
        len += to_write;

        ...
}

Sean

>  
> -- 
> 2.11.0.197.gb556de5.dirty
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Sean Paul, Software Engineer, Google / Chromium OS

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