On 2022-09-19 23:24, Sean Anderson wrote:

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.

Is the DMA controller cache-coherent? I see the mainline LS1046A DT doesn't have a "dma-coherent" property for it, but the behaviour is entirely consistent with that being wrong - dma_map_single() cleans the cache, coherent DMA write hits the still-present cache lines, dma_unmap_single() invalidates the cache, and boom, the data is gone and you read back the previous content of the buffer that was cleaned out to DRAM beforehand.

Robin.

--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;