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

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Message-ID: <dbba9f0c-4621-2d58-8fb8-4cbe788558f9@siemens.com>
Date:   Mon, 24 Aug 2020 14:49:18 +0200
From:   Jan Kiszka <jan.kiszka@...mens.com>
To:     Vignesh Raghavendra <vigneshr@...com>,
        Tudor Ambarus <tudor.ambarus@...rochip.com>,
        Mark Brown <broonie@...nel.org>,
        "Jin, Le (RC-CN DF FA R&D)" <le.jin@...mens.com>
Cc:     Boris Brezillon <bbrezillon@...nel.org>,
        Ramuthevar Vadivel Murugan 
        <vadivel.muruganx.ramuthevar@...ux.intel.com>,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-spi@...r.kernel.org, simon.k.r.goldschmidt@...il.com,
        dinguyen@...nel.org, marex@...x.de
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@...com>
>>> Reviewed-by: Tudor Ambarus <tudor.ambarus@...rochip.com>
>>> ---
> [...]
>>>
>>>  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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