Re: [“PATCH” 2/2] spi: dw: Add support for Intel Thunder Bay SPI

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

On Thu, Jul 22, 2021 at 01:33:58PM +0800, nandhini.srikandan@intel.com wrote:
> From: Nandhini Srikandan <nandhini.srikandan@intel.com>
> 
> Add support for Intel Thunder Bay SPI controller, which uses DesignWare
> DWC_ssi core.
> Bit 31 of CTRLR0 register is added for Thunder Bay, to
> configure the device as a master or as a slave serial peripheral.

> Bit 14(SSTE) of CTRLR0 register should be set(1) for Thunder Bay.

Could you elaborate what this bit mean?

> Added reset of SPI controller required for Thunder Bay.

If it's really required (is it?) then you were supposed to reflect
that in the code by returning a negative error if the driver fails to
retrieve the reset control handler. In accordance with that the
bindings should have been also updated so the dtbs_check procedure
would make sure the Thunder Bay SPI DT-node comply to the requirements
in that matter.

Anyway I've got a few comments regarding this part of your patch.
Please see them below.

> 
> Signed-off-by: Nandhini Srikandan <nandhini.srikandan@intel.com>
> ---
>  drivers/spi/spi-dw-core.c |  6 ++++++
>  drivers/spi/spi-dw-mmio.c | 20 ++++++++++++++++++++
>  drivers/spi/spi-dw.h      | 15 +++++++++++++++
>  3 files changed, 41 insertions(+)
> 
> diff --git a/drivers/spi/spi-dw-core.c b/drivers/spi/spi-dw-core.c
> index a305074c482e..eecf8dcd0677 100644
> --- a/drivers/spi/spi-dw-core.c
> +++ b/drivers/spi/spi-dw-core.c
> @@ -302,6 +302,12 @@ static u32 dw_spi_prepare_cr0(struct dw_spi *dws, struct spi_device *spi)
>  
>  		if (dws->caps & DW_SPI_CAP_KEEMBAY_MST)
>  			cr0 |= DWC_SSI_CTRLR0_KEEMBAY_MST;
> +

> +		if (dws->caps & DW_SPI_CAP_THUNDERBAY_MST)
> +			cr0 |= DWC_SSI_CTRLR0_THUNDERBAY_MST;

I guess that KeemBay and ThunderBay SPI controllers have been
synthesized based on the same IP-core with a few differences. Is that
true? Could you tell us what is the difference between them?

Anyway regarding this the Master/Slave part. Is the ThunderBay
implementation of the Master/Slave capability the same as it was
embedded in the KeemBay controller? If so then what do you think about
just renaming DW_SPI_CAP_KEEMBAY_MST to something like
DW_SPI_CAP_INTEL_MST and using it then for both Keembay and ThunderBay
versions of the SPI-controllers? (The similar renaming needs to be
provided for the DWC_SSI_CTRLR0_KEEMBAY_MST macro then.) You can
implement it as a preparation patch posted before this one in the
series.

> +
> +		if (dws->caps & DW_SPI_CAP_THUNDERBAY_SSTE)
> +			cr0 |= DWC_SSI_CTRLR0_THUNDERBAY_SSTE;

Similar question regarding the SSTE bit. Is it something ThunderBay
specific only? Was the corresponding functionality embedded into the
KeemBay or any other Intel version of the DW SPI controller?

>  	}
>  
>  	return cr0;
> diff --git a/drivers/spi/spi-dw-mmio.c b/drivers/spi/spi-dw-mmio.c
> index 3379720cfcb8..ca9aad078752 100644
> --- a/drivers/spi/spi-dw-mmio.c
> +++ b/drivers/spi/spi-dw-mmio.c
> @@ -222,6 +222,15 @@ static int dw_spi_keembay_init(struct platform_device *pdev,
>  	return 0;
>  }
>  
> +static int dw_spi_thunderbay_init(struct platform_device *pdev,
> +				  struct dw_spi_mmio *dwsmmio)
> +{

> +	dwsmmio->dws.caps = DW_SPI_CAP_THUNDERBAY_MST | DW_SPI_CAP_THUNDERBAY_RST |
> +			    DW_SPI_CAP_THUNDERBAY_SSTE | DW_SPI_CAP_DWC_SSI;
> +

Originally the DW_SPI_CAP-functionality was provided to modify the DW
SPI core driver behavior when it was required. For instance it was
mostly connected with the platform-specific CR0-register
configurations. So as I see it the reset part can be successfully
handled fully in the framework of the MMIO-platform glue-driver.
Instead of defining a new capability you could have just added the
next code in the ThunderBay init-method:

+	if (!dwsmmio->rstc) {
+		dev_err(&pdev->dev, "Reset control is missing\n");
+		return -EINVAL;
+	}
+
+	reset_control_assert(dwsmmio->rstc);
+	udelay(2);
+	reset_control_deassert(dwsmmio->rstc);
+

Thus you'd reuse the already implemented reset-controller handler
defined in the dw_spi_mmio structure with no need of implementing
a new capability.

> +	return 0;
> +}
> +
>  static int dw_spi_canaan_k210_init(struct platform_device *pdev,
>  				   struct dw_spi_mmio *dwsmmio)
>  {
> @@ -243,6 +252,7 @@ static int dw_spi_mmio_probe(struct platform_device *pdev)
>  			 struct dw_spi_mmio *dwsmmio);
>  	struct dw_spi_mmio *dwsmmio;
>  	struct resource *mem;
> +	struct reset_control *rst;
>  	struct dw_spi *dws;
>  	int ret;
>  	int num_cs;
> @@ -309,6 +319,15 @@ static int dw_spi_mmio_probe(struct platform_device *pdev)
>  			goto out;
>  	}
>  

> +	if (dws->caps & DW_SPI_CAP_THUNDERBAY_RST) {
> +		rst = devm_reset_control_get_exclusive(&pdev->dev, NULL);
> +		if (!IS_ERR(rst)) {
> +			reset_control_assert(rst);
> +			udelay(2);
> +			reset_control_deassert(rst);
> +		}
> +	}
> +

Please see my comment above. We don't need to have this code here if
you get to implement what I suggest there.

>  	pm_runtime_enable(&pdev->dev);
>  
>  	ret = dw_spi_add_host(&pdev->dev, dws);
> @@ -349,6 +368,7 @@ static const struct of_device_id dw_spi_mmio_of_match[] = {
>  	{ .compatible = "renesas,rzn1-spi", .data = dw_spi_dw_apb_init},
>  	{ .compatible = "snps,dwc-ssi-1.01a", .data = dw_spi_dwc_ssi_init},
>  	{ .compatible = "intel,keembay-ssi", .data = dw_spi_keembay_init},
> +	{ .compatible = "intel,thunderbay-ssi", .data = dw_spi_thunderbay_init},
>  	{ .compatible = "microchip,sparx5-spi", dw_spi_mscc_sparx5_init},
>  	{ .compatible = "canaan,k210-spi", dw_spi_canaan_k210_init},
>  	{ /* end of table */}
> diff --git a/drivers/spi/spi-dw.h b/drivers/spi/spi-dw.h
> index b665e040862c..bfe1d5edc25a 100644
> --- a/drivers/spi/spi-dw.h
> +++ b/drivers/spi/spi-dw.h
> @@ -82,6 +82,18 @@
>   */
>  #define DWC_SSI_CTRLR0_KEEMBAY_MST	BIT(31)
>  

> +/*
> + * For Thunder Bay, CTRLR0[14] should be set to 1.
> + */

Could you provide a bit more details what this bit has been
implemented for?

> +#define DWC_SSI_CTRLR0_THUNDERBAY_SSTE	BIT(14)
> +

> +/*
> + * For Thunder Bay, CTRLR0[31] is used to select controller mode.
> + * 0: SSI is slave
> + * 1: SSI is master
> + */
> +#define DWC_SSI_CTRLR0_THUNDERBAY_MST	BIT(31)

Please see my suggestion regarding the Master/Slave capability in one
of the comments above.

Regards
-Serge

> +
>  /* Bit fields in CTRLR1 */
>  #define SPI_NDF_MASK			GENMASK(15, 0)
>  
> @@ -125,6 +137,9 @@ enum dw_ssi_type {
>  #define DW_SPI_CAP_KEEMBAY_MST		BIT(1)
>  #define DW_SPI_CAP_DWC_SSI		BIT(2)
>  #define DW_SPI_CAP_DFS32		BIT(3)
> +#define DW_SPI_CAP_THUNDERBAY_MST	BIT(4)
> +#define DW_SPI_CAP_THUNDERBAY_RST	BIT(5)
> +#define DW_SPI_CAP_THUNDERBAY_SSTE	BIT(6)
>  
>  /* Slave spi_transfer/spi_mem_op related */
>  struct dw_spi_cfg {
> -- 
> 2.17.1
>