Re: [PATCH 01/11] spi: dw: define capability for enhanced spi

[Serge Semin <fancer.lancer@gmail.com>]

On Tue, Aug 02, 2022 at 06:57:45PM +0100, Sudip Mukherjee wrote:
> Some Synopsys SSI controllers support enhanced SPI which includes
> Dual mode, Quad mode and Octal mode. Define the capability and mention
> it in the controller supported modes.
> 
> Signed-off-by: Sudip Mukherjee <sudip.mukherjee@sifive.com>
> ---
>  drivers/spi/spi-dw-core.c | 4 ++++
>  drivers/spi/spi-dw.h      | 1 +
>  2 files changed, 5 insertions(+)
> 
> diff --git a/drivers/spi/spi-dw-core.c b/drivers/spi/spi-dw-core.c
> index f87d97ccd2d6..97e72da7c120 100644
> --- a/drivers/spi/spi-dw-core.c
> +++ b/drivers/spi/spi-dw-core.c
> @@ -917,6 +917,10 @@ int dw_spi_add_host(struct device *dev, struct dw_spi *dws)
>  
>  	master->use_gpio_descriptors = true;
>  	master->mode_bits = SPI_CPOL | SPI_CPHA | SPI_LOOP;

> +	if (dws->caps & DW_SPI_CAP_EXT_SPI)
> +		master->mode_bits |= SPI_TX_DUAL | SPI_RX_DUAL |
> +				SPI_TX_QUAD | SPI_RX_QUAD |
> +				SPI_TX_OCTAL | SPI_RX_OCTAL;

Is it possible to auto-detect the highest supported mode by, for
instance, writing to the CTRL0.SPI_FRF field values up to the maximum
one? The DW SSI hardware manual says that the unsupported mode
combinations are reserved. Could the reserved modes still be written
to the SPI_FRF field? If not we could use it to set the
SPI_{TX,RX}_DUAL, SPI_{TX,RX}_QUAD, SPI_{TX,RX}_OCTAL in accordance
with the actual device capabilities rather than setting all of them.

>  	if (dws->caps & DW_SPI_CAP_DFS32)
>  		master->bits_per_word_mask = SPI_BPW_RANGE_MASK(4, 32);
>  	else
> diff --git a/drivers/spi/spi-dw.h b/drivers/spi/spi-dw.h
> index 9e8eb2b52d5c..71d18e9291a3 100644
> --- a/drivers/spi/spi-dw.h
> +++ b/drivers/spi/spi-dw.h
> @@ -32,6 +32,7 @@
>  /* DW SPI controller capabilities */
>  #define DW_SPI_CAP_CS_OVERRIDE		BIT(0)
>  #define DW_SPI_CAP_DFS32		BIT(1)

> +#define DW_SPI_CAP_EXT_SPI		BIT(2)

EXT-prefix is misleading. The feature is called "Enhanced SPI Modes",
not Extended SPI modes. Perhaps something like DW_SPI_CAP_EMODE ?

-Sergey

>  
>  /* Register offsets (Generic for both DWC APB SSI and DWC SSI IP-cores) */
>  #define DW_SPI_CTRLR0			0x00
> -- 
> 2.30.2
>