RE: [EXT] Re: [PATCH v4] spi: imx: fix the burst length at DMA mode and CPU mode

[Carlos Song <carlos.song@xxxxxxx>]

> -----Original Message-----
> From: Benjamin Bigler <benjamin@xxxxxxxxxx>
> Sent: Friday, February 2, 2024 4:15 AM
> To: Carlos Song <carlos.song@xxxxxxx>; broonie@xxxxxxxxxx;
> shawnguo@xxxxxxxxxx; s.hauer@xxxxxxxxxxxxxx; kernel@xxxxxxxxxxxxxx;
> dl-linux-imx <linux-imx@xxxxxxx>; stefanmoring@xxxxxxxxx
> Cc: linux-spi@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx
> Subject: [EXT] Re: [PATCH v4] spi: imx: fix the burst length at DMA mode and
> CPU mode
>
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> On Thu, 2024-02-01 at 18:54 +0800, carlos.song@xxxxxxx wrote:
> > From: Carlos Song <carlos.song@xxxxxxx>
> >
> > For DMA mode, the bus width of the DMA is equal to the size of data
> > word, so burst length should be configured as bits per word.
> >
> > For CPU mode, because of the spi transfer len is in byte, so burst
> > length should be configured as bits per byte * spi_imx->count.
> >
> > Signed-off-by: Carlos Song <carlos.song@xxxxxxx>
> > Reviewed-by: Clark Wang <xiaoning.wang@xxxxxxx>
> > Fixes: e9b220aeacf1 ("spi: spi-imx: correctly configure burst length
> > when using dma")
> > Fixes: 5f66db08cbd3 ("spi: imx: Take in account bits per word instead
> > of assuming 8-bits")
> > ---
> > Changes for V3:
> > - include <linux/bits.h>
> > Changes for V4:
> > - keep the includes sorted alphabetically.
> > ---
> >  drivers/spi/spi-imx.c | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/spi/spi-imx.c b/drivers/spi/spi-imx.c index
> > 546cdce525fc..f7990ac2c654 100644
> > --- a/drivers/spi/spi-imx.c
> > +++ b/drivers/spi/spi-imx.c
> > @@ -2,6 +2,7 @@
> >  // Copyright 2004-2007 Freescale Semiconductor, Inc. All Rights Reserved.
> >  // Copyright (C) 2008 Juergen Beisert
> >
> > +#include <linux/bits.h>
> >  #include <linux/clk.h>
> >  #include <linux/completion.h>
> >  #include <linux/delay.h>
> > @@ -660,15 +661,14 @@ static int mx51_ecspi_prepare_transfer(struct
> spi_imx_data *spi_imx,
> >                       << MX51_ECSPI_CTRL_BL_OFFSET;
> >       else {
> >               if (spi_imx->usedma) {
> > -                     ctrl |= (spi_imx->bits_per_word *
> > -
> spi_imx_bytes_per_word(spi_imx->bits_per_word) - 1)
> > +                     ctrl |= (spi_imx->bits_per_word - 1)
> >                               << MX51_ECSPI_CTRL_BL_OFFSET;
> >               } else {
> >                       if (spi_imx->count >=
> MX51_ECSPI_CTRL_MAX_BURST)
> > -                             ctrl |= (MX51_ECSPI_CTRL_MAX_BURST -
> 1)
> > +                             ctrl |= (MX51_ECSPI_CTRL_MAX_BURST *
> > + BITS_PER_BYTE - 1)
> >                                               <<
> MX51_ECSPI_CTRL_BL_OFFSET;
> >                       else
> > -                             ctrl |= (spi_imx->count *
> spi_imx->bits_per_word - 1)
> > +                             ctrl |= (spi_imx->count * BITS_PER_BYTE
> > + - 1)


Hi,

Thank you! You re right. I have get the patch history that spi->bits_per_word = 9 will
break the driver, this is a special case.

So burst length should be calculated by the number of words, instead of the number of bytes, otherwise the transmission of these non-byte-aligned word will break the driver.

the burst length can be set by:
spi_imx->count/DIV_ROUND_UP(spi_imx->bits_per_word, BITS_PER_BYTE) * spi_imx->bits_per_word.

I will set V5 later.
> I think that will not work for drivers which dont use bits_per_word=8.
> https://lore.ker/
> nel.org%2Fall%2F20230917164037.29284-1-stefanmoring%40gmail.com%2F&
> data=05%7C02%7Ccarlos.song%40nxp.com%7C6f52557285a34b97c6f508dc2
> 3626f51%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C638424152
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> 2kHdgiwqi5yxnDPLwWViplttHA2E05WFZmTuw%3D&reserved=0
> >                                               <<
> MX51_ECSPI_CTRL_BL_OFFSET;
> >               }
> >       }
>
> Best regards,
> Benjamin Bigler