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From:   Sean Anderson <sean.anderson@seco.com>
Subject: [BUG] ls1046a: eDMA does not transfer data from I2C
To:     Oleksij Rempel <linux@rempel-privat.de>,
        Pengutronix Kernel Team <kernel@pengutronix.de>,
        linux-i2c@vger.kernel.org,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        Vinod Koul <vkoul@kernel.org>, dmaengine@vger.kernel.org
Cc:     Sumit Semwal <sumit.semwal@linaro.org>,
        =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org,
        linaro-mm-sig@lists.linaro.org, Joy Zou <joy.zou@nxp.com>,
        Peng Ma <peng.ma@nxp.com>, Robin Gong <yibin.gong@nxp.com>,
        Shawn Guo <shawnguo@kernel.org>, Li Yang <leoyang.li@nxp.com>
Message-ID: <38974aab-06d0-f5ff-d359-5eedd2f3bb3e@seco.com>
Date:   Mon, 19 Sep 2022 18:24:08 -0400
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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;