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Date:   Thu, 22 Jul 2021 21:26:20 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     nandhini.srikandan@...el.com
Cc:     broonie@...nel.org, robh+dt@...nel.org, linux-spi@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        mgross@...ux.intel.com, kris.pan@...el.com,
        kenchappa.demakkanavar@...el.com, furong.zhou@...el.com,
        mallikarjunappa.sangannavar@...el.com, mahesh.r.vaidya@...el.com,
        rashmi.a@...el.com
Subject: Re: [“PATCH” 2/2] spi: dw: Add
 support for Intel Thunder Bay SPI

One more nitpick below.

On Thu, Jul 22, 2021 at 08:04:35PM +0300, Serge Semin wrote:
> On Thu, Jul 22, 2021 at 01:33:58PM +0800, nandhini.srikandan@...el.com wrote:
> > From: Nandhini Srikandan <nandhini.srikandan@...el.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@...el.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);

Please, don't forget to add a header file with udelay() declaration to
this module.

-Sergey

> +	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
> > 

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