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

[Serge Semin <fancer.lancer@xxxxxxxxx>]

Hello Andy,

On Mon, Nov 09, 2020 at 04:36:51PM +0200, Andy Shevchenko wrote:
> 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).

Ok. Thanks for clarifying this. Now I see the way it's working.

-Sergey

> 
> 
> -- 
> With Best Regards,
> Andy Shevchenko