RE: [RESEND PATCH v3 5/8] mtd: spi-nor: cadence-quadspi: Handle probe deferral while requesting DMA channel

[Jin, Le]

Hello Jan,

The flash on our board is Winbond W25Q128JV.

Best Regards,
Le Jin

-----Original Message-----
From: Kiszka, Jan (CT RDA IOT SES-DE) <jan.kiszka@xxxxxxxxxxx> 
Sent: Monday, August 24, 2020 8:49 PM
To: Vignesh Raghavendra <vigneshr@xxxxxx>; Tudor Ambarus <tudor.ambarus@xxxxxxxxxxxxx>; Mark Brown <broonie@xxxxxxxxxx>; Jin, Le (RC-CN DI FA R&D SW) <le.jin@xxxxxxxxxxx>
Cc: Boris Brezillon <bbrezillon@xxxxxxxxxx>; Ramuthevar Vadivel Murugan <vadivel.muruganx.ramuthevar@xxxxxxxxxxxxxxx>; linux-mtd@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-spi@xxxxxxxxxxxxxxx; simon.k.r.goldschmidt@xxxxxxxxx; dinguyen@xxxxxxxxxx; marex@xxxxxxx
Subject: Re: [RESEND PATCH v3 5/8] mtd: spi-nor: cadence-quadspi: Handle probe deferral while requesting DMA channel

On 24.08.20 13:45, Vignesh Raghavendra wrote:
> 
> 
> On 8/22/20 11:35 PM, Jan Kiszka wrote:
>> On 01.06.20 09:04, Vignesh Raghavendra wrote:
>>> dma_request_chan_by_mask() can throw EPROBE_DEFER if DMA provider is 
>>> not yet probed. Currently driver just falls back to using PIO mode 
>>> (which is less efficient) in this case. Instead return probe 
>>> deferral error as is so that driver will be re probed once DMA 
>>> provider is available.
>>>
>>> Signed-off-by: Vignesh Raghavendra <vigneshr@xxxxxx>
>>> Reviewed-by: Tudor Ambarus <tudor.ambarus@xxxxxxxxxxxxx>
>>> ---
> [...]
>>>
>>>  static const struct spi_nor_controller_ops cqspi_controller_ops = { 
>>> @@ -1269,8 +1274,11 @@ static int cqspi_setup_flash(struct cqspi_st *cqspi, struct device_node *np)
>>>  			dev_dbg(nor->dev, "using direct mode for %s\n",
>>>  				mtd->name);
>>>
>>> -			if (!cqspi->rx_chan)
>>> -				cqspi_request_mmap_dma(cqspi);
>>> +			if (!cqspi->rx_chan) {
>>> +				ret = cqspi_request_mmap_dma(cqspi);
>>> +				if (ret == -EPROBE_DEFER)
>>> +					goto err;
>>> +			}
>>>  		}
>>>  	}
>>>
>>>
>>
>> This seem to break reading the SPI flash on our IOT2050 [1] (didn't 
>> test the eval board yet).
>>
>> Without that commit, read happens via PIO, and that works. With the 
>> commit, the pattern
>>
>> with open("out.bin", "wb") as out:
>>     pos = 0
>>     while pos < 2:
>>         with open("/dev/mtd0", "rb") as mtd:
>>            mtd.seek(pos * 0x10000)
>>            out.write(mtd.read(0x10000))
>>         pos += 1
>>
>> gives the wrong result for the second block while
> 
> Interesting... Could you please explain wrong result? Is the data move 
> around or completely garbage?

It looks like some stripes contain data from other parts of the flash or kernel RAM. It's not just garbage, there are readable strings included.

> 
> Does this fail even on AM654 EVM? Could you share full script for me 
> to test locally?

The scripts are complete (python). Just binary-diff the outputs.

I'll try on the EVM later.

> 
> What is the flash on the board?

Le, could you answer that more precisely than I could?

Thanks,
Jan

> 
>>
>> with open("out2.bin", "wb") as out:
>>     with open("/dev/mtd0", "rb") as mtd:
>>         out.write(mtd.read(0x20000))
>>
>> (or "mtd_debug read") is fine.
>>
>> What could be the reason? Our DTBs and k3-am654-base-board.dtb had 
>> some deviations /wrt the ospi node, but aligning ours to the base 
>> board made no difference.
>>
>> Jan
>>
>> [1] https://github.com/siemens/linux/commits/jan/iot2050
>>

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Siemens AG, Corporate Technology, CT RDA IOT SES-DE Corporate Competence Center Embedded Linux