[PATCH 08/11] MTD: m25p80: Add option to limit SPI transfer size.

[Michal Suchanek]

On 24 July 2015 at 10:34, Marek Vasut <marex at denx.de> wrote:
> On Thursday, July 23, 2015 at 07:03:47 PM, Michal Suchanek wrote:
>
> Hi!
>
> [...]
>
>> >>> It's probably slower to set up DMA for 2-byte commands but it might
>> >>> work nonetheless.
>> >>
>> >> It is, the overhead will be considerable. It might help the stability
>> >> though. I'm really looking forward to the results!
>> >
>> > Hello,
>> >
>> > this does not quite work.
>> >
>> > My test with spidev:
>> >
>> > # ./spinor /dev/spidev1.0
>> > Sending 9f 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>> > Received 00 ff c8 60 16 c8 60 16 c8 60 16 c8 60 16 c8 60
>> > Sending 90 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>> > Received 00 ff ff ff ff c8 15 c8 15 c8 15 c8 15 c8 15 c8
>> > Sending 9f 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>> > Received 00 ff c8 60 16 c8 60 16 c8 60 16 c8 60 16 c8 60
>> >
>> > I receive correct ID but spi-nor complains it does not know ID 00 c8 60.
>> > IIRC garbage should be sent only at the time command is transferred so
>> > only one byte of garbage should be received. Also the garbage tends to
>> > be the last state of the data output - all 0 or all 1.
>> > So it seems using DMA for all transfers including 1-byte commands
>> > results in (some?) received data getting an extra 00 prefix.
>> >
>> >
>> > I also managed to lock up the controller completely since there is
>> > some error passing the SPI speed somewhere :(
>> >
>> > [ 1352.977530] spidev spi1.0: setup mode 0, 8 bits/w, 80000000 Hz max -->
>> > 0 [ 1352.977540] spidev spi1.0: spi mode 0
>> > [ 1352.977576] spidev spi1.0: setup mode 0, 8 bits/w, 80000000 Hz max -->
>> > 0 [ 1352.977582] spidev spi1.0: msb first
>> > [ 1352.977614] spidev spi1.0: setup mode 0, 8 bits/w, 80000000 Hz max -->
>> > 0 [ 1352.977620] spidev spi1.0: 0 bits per word
>> > [ 1352.977652] spidev spi1.0: setup mode 0, 8 bits/w, 2690588672 Hz max
>> > --> 0 [ 1352.977726] spi_master spi1: s3c64xx_spi_config: clk_from_cmu 1
>> > src_clk sclk_spi1 mode bpw 8
>> > [ 1352.977753] spi_master spi1: spi1.0 s3c64xx_spi_transfer_one: xfer
>> > bpw 8 speed -1604378624
>> > [ 1352.977760] spi_master spi1: s3c64xx_spi_config: clk_from_cmu 1
>> > src_clk sclk_spi1 mode bpw 8
>> > [ 1352.977781] spi_master spi1: spi1.0 s3c64xx_spi_transfer_one: using
>> > dma [ 1352.977797] dma-pl330 121b0000.pdma: setting up request on thread
>> > 1
>>
>> Hmm, on a second thought it probably works as expected more or less.
>>
>> The nonsensical value was passed from application and there is no
>> guard against that.
>>
>> Since I don't do PIO the controller remains locked up indefinitely.
>
> I have to admit, I don't quite understand the above. I also don't quite know
> what your spidev test does.

It does a full duplex transfer sending what is printed and printing
what is received.

> Can you possibly just bind a regular SPI NOR driver
> and run mtdtests to see if it is stable ?

I can if I use PIO for short transfers. Using DMA for all transfers
results in the received data prefixed with 00 so the NOR flash
identification fails. Admittedly I have no idea what the flash memory
actually contains so if all DMA reads were always prefixed with 00 I
could not tell. I vaguely recall reading the whole content and parsing
the

I can probably make the minimum length for DMA configurable so I can
fall back to PIO when the controler locks up. It seems setting up a
PIO transfer makes it work again.

Thanks

Michal