Re: [PATCH v3 24/24] drm/rockchip: dw-mipi-dsi: support read commands

Sean Paul
2017-01-30T15:26:11Z

On Sun, Jan 29, 2017 at 01:24:44PM +0000, John Keeping wrote:
> I haven't found any method for getting the length of a response, so this
> just uses the requested rx_len
>
> Signed-off-by: John Keeping <john@metanate.com>
> ---
> v3:
> - Fix checkpatch warnings
> Unchanged in v2
>
> drivers/gpu/drm/rockchip/dw-mipi-dsi.c | 56 ++++++++++++++++++++++++++++++++++
> 1 file changed, 56 insertions(+)
>
> diff --git a/drivers/gpu/drm/rockchip/dw-mipi-dsi.c b/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
> index cf3ca6b0cbdb..cc58ada75425 100644
> --- a/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
> +++ b/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
> @@ -678,6 +678,56 @@ static int dw_mipi_dsi_dcs_long_write(struct dw_mipi_dsi *dsi,
> return dw_mipi_dsi_gen_pkt_hdr_write(dsi, hdr_val);
> }
>
> +static int dw_mipi_dsi_dcs_read(struct dw_mipi_dsi *dsi,
> + const struct mipi_dsi_msg *msg)
> +{
> + const u8 *tx_buf = msg->tx_buf;
> + u8 *rx_buf = msg->rx_buf;
> + size_t i;
> + int ret, val;
> +
> + dsi_write(dsi, DSI_PCKHDL_CFG, EN_CRC_RX | EN_ECC_RX | EN_BTA);
> + dsi_write(dsi, DSI_GEN_HDR,
> + GEN_HDATA(tx_buf[0]) | GEN_HTYPE(msg->type));
> +
> + ret = readl_poll_timeout(dsi->base + DSI_CMD_PKT_STATUS,
> + val, !(val & GEN_RD_CMD_BUSY), 1000,
> + CMD_PKT_STATUS_TIMEOUT_US);
> + if (ret < 0) {
> + dev_err(dsi->dev, "failed to read command response\n");
> + return ret;
> + }
> +
> + for (i = 0; i < msg->rx_len;) {
> + u32 pld = dsi_read(dsi, DSI_GEN_PLD_DATA);
> +
> + while (i < msg->rx_len) {
> + rx_buf[i] = pld & 0xff;
> + pld >>= 8;
> + i++;
> + }
> + }

AFAICT, the outer for loop just initializes i and ensures msg->rx_len is
non-zero?

I think the following would be easier to read (and safe against the case where
msg->rx_len > sizeof(pld) (even though this shouldn't happen according to DCS
spec)).

if (msg->rx_len > 0) {
u32 pld = dsi_read(dsi, DSI_GEN_PLD_DATA);
memcpy(rx_buf, &pld, MIN(msg->rx_len, sizeof(pld));
}

> +
> + return msg->rx_len;
> +}
> +
> +static int dw_mipi_dsi_set_max_return_packet_size(struct dw_mipi_dsi *dsi,
> + size_t len)
> +{
> + u8 val[] = { len & 0xff, (len >> 8) & 0xff };
> + struct mipi_dsi_msg msg = {
> + .channel = dsi->channel,
> + .type = MIPI_DSI_SET_MAXIMUM_RETURN_PACKET_SIZE,
> + .tx_buf = val,
> + .tx_len = 2,
> + };
> +
> + if (len > 0xffff)
> + return -EINVAL;
> +
> + return dw_mipi_dsi_dcs_short_write(dsi, &msg);
> +}
> +
> static ssize_t dw_mipi_dsi_host_transfer(struct mipi_dsi_host *host,
> const struct mipi_dsi_msg *msg)
> {
> @@ -695,6 +745,12 @@ static ssize_t dw_mipi_dsi_host_transfer(struct mipi_dsi_host *host,
> case MIPI_DSI_DCS_LONG_WRITE:
> ret = dw_mipi_dsi_dcs_long_write(dsi, msg);
> break;
> + case MIPI_DSI_DCS_READ:
> + ret = dw_mipi_dsi_set_max_return_packet_size(dsi, msg->rx_len);
> + if (ret < 0)
> + return ret;
> + ret = dw_mipi_dsi_dcs_read(dsi, msg);
> + break;
> default:
> dev_err(dsi->dev, "unsupported message type 0x%02x\n",
> msg->type);
> --
> 2.11.0.197.gb556de5.dirty
>
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--
Sean Paul, Software Engineer, Google / Chromium OS