Re: [PATCH v2 2/3] spi: Add HiSilicon v3xx SPI NOR flash controller driver

[Andy Shevchenko]

On Fri, Jan 31, 2020 at 2:03 PM John Garry <john.garry@xxxxxxxxxx> wrote:
> On 31/01/2020 11:39, Andy Shevchenko wrote:
> > On Fri, Jan 31, 2020 at 12:08 PM John Garry <john.garry@xxxxxxxxxx> wrote:
> >> On 13/01/2020 14:34, Andy Shevchenko wrote:

...

> >> About this topic of ACPI having no method to describe device buswidth in
> >> the resource descriptor, it may be an idea for me to raise a Tianocore
> >> feature request @ https://bugzilla.tianocore.org/
> >>
> >
> > The 19.6.126 describes the SPI resource, in particular:
> >
> > ---8<---8<---
> > 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.
> > ---8<---8<---
> >
> > 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.

> So how do you find that most firmwares abuse this field? AFAICS, linux
> kernel doesn't interpret this field at all.

>From all tables I have this is the result of appearance (some of the
tables are like 10x times present in my data base, but nevertheless)

    140 SpiSerialBusV2(0x0000,PolarityHigh,FourWireMode,0x08,
   411 SpiSerialBusV2(0x0000,PolarityLow,FourWireMode,0x08,
     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.

We may teach kernel to get something meaningful out of it.

-- 
With Best Regards,
Andy Shevchenko