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

[John Garry]

On 31/01/2020 15:46, Andy Shevchenko wrote:
> 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<---

Hi Andy,

> > > 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.

It seems that someone already had a go at that:
https://lore.kernel.org/lkml/20170317212143.bogj6efzyvvf24yd@xxxxxxxxxxxxx/

Thanks,
John