[BUG] ls1046a: eDMA does not transfer data from I2C

Sean Anderson
2022-09-19T22:24:21Z

Hi all,

I discovered a bug in either imx_i2c or fsl-edma on the LS1046A where no
data is read in i2c_imx_dma_read except for the last two bytes (which
are not read using DMA). This is perhaps best illustrated with the
following example:

# hexdump -C /sys/bus/nvmem/devices/0-00540/nvmem
[ 308.914884] i2c i2c-0: ffff000809380000 0x0000000889380000 0x00000000f5401000 ffff000075401000
[ 308.923529] src= 2180004 dst=f5401000 attr= 0 soff= 0 nbytes=1 slast= 0
[ 308.923529] citer= 7e biter= 7e doff= 1 dlast_sga= 0
[ 308.923529] major_int=1 disable_req=1 enable_sg=0
[ 308.942113] fsl-edma 2c00000.edma: vchan 000000001b4371fc: txd 00000000d9dd26c5[4]: submitted
[ 308.974049] fsl-edma 2c00000.edma: txd 00000000d9dd26c5[4]: marked complete
[ 308.981339] i2c i2c-0: ffff000809380000 = [2e 2e 2f 2e 2e 2f 2e 2e 2f 64 65 76 69 63 65 73 2f 70 6c 61 74 66 6f 72 6d 2f 73 6f 63 2f 32 31 38 30 30 30 30 2e 69 32 63 2f 69 32 63 2d 30 2f 30 2d 30 30 35 34 2f 30 2d 30 30 35 34 30 00 00]
[ 309.002226] i2c i2c-0: ffff000075401000 = [2e 2e 2f 2e 2e 2f 2e 2e 2f 64 65 76 69 63 65 73 2f 70 6c 61 74 66 6f 72 6d 2f 73 6f 63 2f 32 31 38 30 30 30 30 2e 69 32 63 2f 69 32 63 2d 30 2f 30 2d 30 30 35 34 2f 30 2d 30 30 35 34 30 00 00]
[ 309.024649] i2c i2c-0: ffff000809380080 0x0000000889380080 0x00000000f5401800 ffff000075401800
[ 309.033270] src= 2180004 dst=f5401800 attr= 0 soff= 0 nbytes=1 slast= 0
[ 309.033270] citer= 7e biter= 7e doff= 1 dlast_sga= 0
[ 309.033270] major_int=1 disable_req=1 enable_sg=0
[ 309.051633] fsl-edma 2c00000.edma: vchan 000000001b4371fc: txd 00000000d9dd26c5[5]: submitted
[ 309.083526] fsl-edma 2c00000.edma: txd 00000000d9dd26c5[5]: marked complete
[ 309.090807] i2c i2c-0: ffff000809380080 = [00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00]
[ 309.111694] i2c i2c-0: ffff000075401800 = [00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00]
00000000 2e 2e 2f 2e 2e 2f 2e 2e 2f 64 65 76 69 63 65 73 |../../../devices|
00000010 2f 70 6c 61 74 66 6f 72 6d 2f 73 6f 63 2f 32 31 |/platform/soc/21|
00000020 38 30 30 30 30 2e 69 32 63 2f 69 32 63 2d 30 2f |80000.i2c/i2c-0/|
00000030 30 2d 30 30 35 34 2f 30 2d 30 30 35 34 30 00 00 |0-0054/0-00540..|
00000040 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
00000070 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ff ff |................|
00000080 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
*
000000f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ff 5b |...............[|
00000100

(patch with my debug prints appended below)

Despite the DMA completing successfully, no data was copied into the
buffer, leaving the original (now junk) contents. I probed the I2C bus
with an oscilloscope, and I verified that the transfer did indeed occur.
The timing between submission and completion seems reasonable for the
bus speed (50 kHz for whatever reason).

I had a look over the I2C driver, and nothing looked obviously
incorrect. If anyone has ideas on what to try, I'm more than willing.

--Sean

diff --git a/drivers/dma/fsl-edma-common.c b/drivers/dma/fsl-edma-common.c
index 15896e2413c4..1d9d4a55d2af 100644
--- a/drivers/dma/fsl-edma-common.c
+++ b/drivers/dma/fsl-edma-common.c
@@ -391,6 +391,12 @@ void fsl_edma_fill_tcd(struct fsl_edma_hw_tcd *tcd, u32 src, u32 dst,
{
u16 csr = 0;

+ pr_info("src=%8x dst=%8x attr=%4x soff=%4x nbytes=%u slast=%8x\n"
+ "citer=%4x biter=%4x doff=%4x dlast_sga=%8x\n"
+ "major_int=%d disable_req=%d enable_sg=%d\n",
+ src, dst, attr, soff, nbytes, slast, citer, biter, doff,
+ dlast_sga, major_int, disable_req, enable_sg);
+
/*
* eDMA hardware SGs require the TCDs to be stored in little
* endian format irrespective of the register endian model.
diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
index 3576b63a6c03..0217f0cb1331 100644
--- a/drivers/i2c/busses/i2c-imx.c
+++ b/drivers/i2c/busses/i2c-imx.c
@@ -402,6 +402,9 @@ static int i2c_imx_dma_xfer(struct imx_i2c_struct *i2c_imx,
dev_err(dev, "DMA mapping failed\n");
goto err_map;
}
+ phys_addr_t bufp = virt_to_phys(msgs->buf);
+ dev_info(dev, "%px %pap %pad %px\n", msgs->buf, &bufp,
+ &dma->dma_buf, phys_to_virt(dma->dma_buf));

txdesc = dmaengine_prep_slave_single(dma->chan_using, dma->dma_buf,
dma->dma_len, dma->dma_transfer_dir,
@@ -965,6 +968,9 @@ static int i2c_imx_dma_read(struct imx_i2c_struct *i2c_imx,
}
schedule();
}
+ dev_info(dev, "%px = [%*ph]\n", msgs->buf, msgs->len, msgs->buf);
+ dev_info(dev, "%px = [%*ph]\n", phys_to_virt(dma->dma_buf), msgs->len,
+ phys_to_virt(dma->dma_buf));

temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2CR);
temp &= ~I2CR_DMAEN;