Re: [PATCH 0/4] spi-mem: Allow specifying the byte order in DTR mode

[<Tudor.Ambarus@xxxxxxxxxxxxx>]

On 2/21/22 09:44, Michael Walle wrote:
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> Am 2022-02-18 15:58, schrieb Tudor Ambarus:
>> Fortunately there are controllers
>> that can swap back the bytes at runtime, fixing the endiannesses.
>> Provide
>> a way for the upper layers to specify the byte order in DTR mode.
> 
> Are there any patches for the atmel-quadspi yet? What happens if

not public, but will publish them these days.

> the controller doesn't support it? Will there be a software fallback?

no need for a fallback, the controller can ignore op->data.dtr_bswap16 if
it can't swap bytes.

Here's the changes that enable this on atmel-quadspi:

Author: Tudor Ambarus <tudor.ambarus@xxxxxxxxxxxxx>
Date:   Thu Feb 17 10:48:10 2022 +0200

    spi: atmel-quadspi: Set endianness on 8D-8D-8D mode according to the flash requirements
    
    Macronix swaps bytes on a 16-bit boundary when configured in Octal DTR.
    The byte order of 16-bit words is swapped when read or write written in
    8D-8D-8D mode compared to STR modes. Set the endianness flash requirements
    to avoid endianness problems during boot stages.
    
    Signed-off-by: Tudor Ambarus <tudor.ambarus@xxxxxxxxxxxxx>

diff --git a/drivers/spi/atmel-quadspi.c b/drivers/spi/atmel-quadspi.c
index a4ba94ce84f1..c4a3963f7c84 100644
--- a/drivers/spi/atmel-quadspi.c
+++ b/drivers/spi/atmel-quadspi.c
@@ -697,6 +697,8 @@ static int atmel_qspi_sama7g5_set_cfg(struct atmel_qspi *aq,
                ifr |= QSPI_IFR_DDREN;
                if (op->cmd.dtr)
                        ifr |= QSPI_IFR_DDRCMDEN;
+               if (op->data.dtr_bswap16)
+                       ifr |= QSPI_IFR_END;
 
                ifr |= QSPI_IFR_DQSEN;
        }