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

On Tue, Jan 31, 2017 at 12:41:47PM +0000, John Keeping wrote:

On Mon, 30 Jan 2017 15:16:09 -0500, Sean Paul wrote:

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On Mon, Jan 30, 2017 at 06:14:27PM +0000, John Keeping wrote:

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On Mon, 30 Jan 2017 10:26:11 -0500, Sean Paul wrote:

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On Sun, Jan 29, 2017 at 01:24:44PM +0000, John Keeping wrote:

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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)); }

I think the intent was to handle rx_len > 4, but the patch is obvously completely broken regarding that. As far as I can tell, rx_len is limited by the maximum return packet size which can be any value up to the maximum size of a long packet, so we may need to read from the FIFO multiple times.

The loop should be something like this:

for (i = 0; i < msg->rx_len;) { u32 pld = dsi_read(dsi, DSI_GEN_PLD_DATA); int j;

for (j = 0; j < 4 && i < msg->rx_len; i++, j++) {
	rx_buf[i] = pld & 0xff;
	pld >>= 8;
}

}

Short packets should never exceed 32 bits, so I don't think you need to add the nested loop.

The read response is not restricted to a short packet. I have a panel that documents a read request that returns up to 64KiB, admittedly with a continuation command and the panels I have seem to only be programmed to return 5 bytes of meaningful data, but they do return all of those bytes in a single read response.

Ah, apologies for the misunderstanding. In that case, I think you can get away with replacing the inner loop in your snippet with a memcpy and call it a day.

Sean

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