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

Sean Anderson
2022-09-22T23:10:16Z

On 9/20/22 7:05 PM, Sean Anderson wrote:
>
>
> On 9/20/22 6:49 PM, Leo Li wrote:
>>
>>
>>> -----Original Message-----
>>> From: Sean Anderson <sean.anderson@seco.com>
>>> Sent: Tuesday, September 20, 2022 11:21 AM
>>> To: Robin Murphy <robin.murphy@arm.com>; 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; Leo Li <leoyang.li@nxp.com>; Laurentiu Tudor
>>> <laurentiu.tudor@nxp.com>
>>> Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>; dri-
>>> devel@lists.freedesktop.org; Christian König <christian.koenig@amd.com>;
>>> linaro-mm-sig@lists.linaro.org; Shawn Guo <shawnguo@kernel.org>; Sumit
>>> Semwal <sumit.semwal@linaro.org>; Joy Zou <joy.zou@nxp.com>; linux-
>>> media@vger.kernel.org
>>> Subject: Re: [BUG] ls1046a: eDMA does not transfer data from I2C
>>>
>>>
>>>
>>> On 9/20/22 11:44 AM, Sean Anderson wrote:
>>> >
>>> >
>>> > On 9/20/22 11:24 AM, Sean Anderson wrote:
>>> >>
>>> >>
>>> >> On 9/20/22 6:07 AM, Robin Murphy wrote:
>>> >>> 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.
>>> >>
>>> >> I've tried both with and without [1] applied. I also tried removing
>>> >> the call to dma_unmap_single, but to no effect.
>>> >
>>> > Actually, I wasn't updating my device tree like I thought...
>>> >
>>> > Turns out I2C works only *without* this patch.
>>> >
>>> > So maybe the eDMA is not coherent?
>>>
>>> It seems like this might be the case. From the reference manual:
>>>
>>> > All transactions from eDMA are tagged as snoop configuration if the
>>> > SCFG_SNPCNFGCR[eDMASNP] bit is set. Refer Snoop Configuration
>>> Register
>>> > (SCFG_SNPCNFGCR) for details.
>>>
>>> But there is no such bit in this register on the LS1046A. On the LS1043A, this
>>> bit does exist, but on the LS1046A it is reserved. I read the register, and
>>> found the bit was 0. Perhaps eDMA was intended to be coherent, but there
>>> was a hardware bug?
>>
>> Thanks for the findings. I don't know the reason why this bit is reserved on LS1046a either. It should have a similar design as LS1043a.
>
> Funnily enough, this bit is not set for the LS1043A either [1]. So maybe
> this is a U-Boot bug? I'll test this tomorrow.

OK, this looks like it fixes things. I'll submit a patch to U-Boot. But
this bit should really be documented in the LS1046A manual as well.

--Sean

> [1] https://source.denx.de/u-boot/u-boot/-/blob/master/arch/arm/cpu/armv8/fsl-layerscape/soc.c#L680
>
>>>
>>> If this is the case, then I think dma-coherent should be left out of the top-
>>> level /soc node. Instead, the qdma, sata, usb, and emmc nodes should have
>>> dma-coherent added.
>>>
>>> Li/Laurentiu, what are your thoughts?
>>
>> Then looks like it is not correct to say all devices on the bus is coherent. But as we have the new "dma-noncoherent" property now and most of the devices are actually coherent, we probably can keep the bus as dma-coherent and mark exceptions with dma-noncoherent?
>
> Neat, I didn't know about that.
>
> Yes, that sounds good. For the moment, only i2c0 uses DMA, so we will
> only need it there. At some point, someone should send a patch enabling
> it for the rest of the I2C devices, as well as the LPUARTs and SPIs.