On Fri, Jan 31, 2020 at 05:46:39PM +0200, Andy Shevchenko wrote:
> On Fri, Jan 31, 2020 at 2:03 PM John Garry <john.garry@huawei.com> wrote:
> > On 31/01/2020 11:39, Andy Shevchenko wrote:

> > > DataBitLength is the size, in bits, of the smallest transfer unit for
> > > this connection. _LEN is automatically
> > > created to refer to this portion of the resource descriptor.

> > > Is it what you are looking for? (As far as I know most of the
> > > firmwares simple abuse this field among others)

> > I didn't think so - I thought that there was a distinction between width
> > and length in SPI terms.

> My interpretation of this field is a data width of the slave.
> Basically what we have as transfer->size inside SPI in the Linux
> kernel.

This discussion is about the number of data lines, SPI_TX_QUAD
and friends.

>      1 SpiSerialBusV2(0x0000,PolarityLow,FourWireMode,0x08,
>     36 SpiSerialBusV2(0x0000,PolarityLow,FourWireMode,0x10,
>     35 SpiSerialBusV2(0x0000,PolarityLow,FourWireMode,0x18,
>     35 SpiSerialBusV2(0x0000,PolarityLow,FourWireMode,0x20,
>      1 SpiSerialBusV2(0x0000,PolarityLow,ThreeWireMode,0x10,
>      8 SpiSerialBusV2(0x0001,PolarityLow,FourWireMode,0x08,
>      1 SpiSerialBusV2(0x0001,PolarityLow,FourWireMode,0x10,

> So, it seems I stand corrected, the field is in right use, although
> cases like 0x10 and 0x20 should be carefully checked.

Those look like they're mainly controlling SPI_3WIRE so it does
look like a reasonable fit, yes.