Re: [PATCH 02/32] spi: dw: Add support for 32-bits ctrlr0 layout

[Andy Shevchenko <andy.shevchenko@xxxxxxxxx>]

On Mon, Nov 9, 2020 at 4:25 PM Serge Semin <fancer.lancer@xxxxxxxxx> wrote:
>
> Hello Damien,
> Thanks for your patches. My comments are below.
>
> On Sat, Nov 07, 2020 at 05:13:50PM +0900, Damien Le Moal wrote:
> > Synopsis DesignWare DW_apb_ssi version 4 defines a 32-bit layout of
> > the ctrlr0 register for SPI masters. The layout of ctrlr0 is:
> >
> > |   31 .. 23  | 22 .. 21 | 20 .. 16 |
> > | other stuff | spi_frf  |  dfs_32  |
> >
> > |   15 .. 10  | 9 .. 8 | 7 .. 6 | 5 .. 4 | 3 .. 0 |
> > | other stuff |  tmod  |  mode  |  frf   |  dfs   |
> >
>
> > Th main difference of this layout with the 16-bits version is the data
>     ^
>     |
>     e
>
> > frame format field which resides in bits 16..20 instead of bits 3..0.
> >
>
> Are you sure they have been moved from [0, 3] to [16, 20]? I don't have the
> manual for the 4.0x version of the core, but according to this patch:
> https://patchwork.kernel.org/project/spi-devel-general/patch/1575907443-26377-7-git-send-email-wan.ahmad.zainie.wan.mohamad@xxxxxxxxx/
> it has been ok to use the lowest four bits for DFS setting. Is the commit
> message misleading there?

20:16 DFS_32
Data Frame Size in 32-bit transfer size mode. Used to select
the data frame size in 32-bit transfer mode. These bits are
only valid when SSI_MAX_XFER_SIZE is configured to 32.
When the data frame size is programmed to be less than 32
bits, the receive data are automatically right-justified by the
receive logic, with the upper bits of the receive FIFO zero-
padded.

3:0 DFS
Data Frame Size.
This register field is only valid when SSI_MAX_XFER_SIZE
is configured to 16. If SSI_MAX_XFER_SIZE is configured to
32, then writing to this field will not have any effect.

As far as I can tell it's an extension to the existing one (which one
in use depends on the SSI configuration).


The comment you are referring to is about DW_ssi v1.x (vs. DW_apb_ssi v4.x).


-- 
With Best Regards,
Andy Shevchenko