[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:

quoted

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

quoted

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

quoted

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

quoted

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 <redacted>
---
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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-- 
Sean Paul, Software Engineer, Google / Chromium OS