Re: [PATCH 1/3] spi: dw: Add support for 32-bits max xfer size

[Sean Anderson <seanga2@gmail.com>]

On 11/25/20 2:52 PM, Serge Semin wrote:
> Damien,
> 
> Thanks for sending the patch. My comments are below.
> 
> On Thu, Nov 19, 2020 at 09:02:51PM +0900, Damien Le Moal wrote:
>> Synopsis DesignWare DW_apb_ssi version 3.23 onward defines a 32-bits
>> maximum transfer size synthesis parameter (SSI_MAX_XFER_SIZE=32) in
>> addition to the legacy 16-bits configuration (SSI_MAX_XFER_SIZE=16) for
>> SPI controllers.  When SSI_MAX_XFER_SIZE=32, the layout of the ctrlr0
>> register changes and RX/TX FIFO words can be up to 32-bits.
>>
>> The layout of ctrlr0 change for the 32-bits configuration moves the
>> data frame format field to bits 16..20 instead of bits 3..0
>> when the controller is configured with SSI_MAX_XFER_SIZE=16.
>>
>> Introduce the DW SPI capability flag DW_SPI_CAP_DWC_APB_XFER32 to
>> indicate in that the controller is configured with SSI_MAX_XFER_SIZE=32.
>> Since the SSI_MAX_XFER_SIZE parameter is a controller synthesis
>> parameter not accessible through a register, the detection of this
>> parameter value is done in spi_hw_init() by writing and reading the
>> ctrlr0 register and testing the value of bits 20..16.
>>
>> The DW_SPI_CAP_DWC_APB_XFER32 flag is used in dw_spi_update_config() to
>> set the data frame size field at the correct position and in
>> dw_spi_add_host() to extend bits_per_word_mask to 32-bits.
>> dw_reader() and dw_writer() are also modified to handle 32-bits FIFO
>> words.
>>
>> Suggested-by: Sean Anderson <seanga2@gmail.com>
>> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
>> ---
>>   drivers/spi/spi-dw-core.c | 40 ++++++++++++++++++++++++++++++++-------
>>   drivers/spi/spi-dw.h      |  8 ++++++++
>>   2 files changed, 41 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/spi/spi-dw-core.c b/drivers/spi/spi-dw-core.c
>> index 2e50cc0a9291..4c16832b16fd 100644
>> --- a/drivers/spi/spi-dw-core.c
>> +++ b/drivers/spi/spi-dw-core.c
>> @@ -137,14 +137,16 @@ static inline u32 rx_max(struct dw_spi *dws)
>>   static void dw_writer(struct dw_spi *dws)
>>   {
>>   	u32 max = tx_max(dws);
>> -	u16 txw = 0;
>> +	u32 txw = 0;
>>   
>>   	while (max--) {
>>   		if (dws->tx) {
>>   			if (dws->n_bytes == 1)
>>   				txw = *(u8 *)(dws->tx);
>> -			else
>> +			else if (dws->n_bytes == 2)
>>   				txw = *(u16 *)(dws->tx);
>> +			else
>> +				txw = *(u32 *)(dws->tx);
>>   
>>   			dws->tx += dws->n_bytes;
>>   		}
>> @@ -156,15 +158,17 @@ static void dw_writer(struct dw_spi *dws)
>>   static void dw_reader(struct dw_spi *dws)
>>   {
>>   	u32 max = rx_max(dws);
>> -	u16 rxw;
>> +	u32 rxw;
>>   
>>   	while (max--) {
>>   		rxw = dw_read_io_reg(dws, DW_SPI_DR);
>>   		if (dws->rx) {
>>   			if (dws->n_bytes == 1)
>>   				*(u8 *)(dws->rx) = rxw;
>> -			else
>> +			else if (dws->n_bytes == 2)
>>   				*(u16 *)(dws->rx) = rxw;
>> +			else
>> +				*(u32 *)(dws->rx) = rxw;
>>   
>>   			dws->rx += dws->n_bytes;
>>   		}
>> @@ -311,8 +315,12 @@ void dw_spi_update_config(struct dw_spi *dws, struct spi_device *spi,
>>   	u32 speed_hz;
>>   	u16 clk_div;
>>   
> 
>> -	/* CTRLR0[ 4/3: 0] Data Frame Size */
>> -	cr0 |= (cfg->dfs - 1);
>> +	if (!(dws->caps & DW_SPI_CAP_DWC_APB_XFER32))
>> +		/* CTRLR0[ 4/3: 0] Data Frame Size */
>> +		cr0 |= (cfg->dfs - 1);
>> +	else
>> +		/* CTRLR0[20: 16] Data Frame Size */
>> +		cr0 |= FIELD_PREP(DWC_APB_CTRLR0_DFS32_MASK, cfg->dfs - 1);
> 
> Instead of constantly checking the capability flag here I'd suggest to add
> a new dfs_off member to the private data. Like this:
> --- a/drivers/spi/spi-dw.h
> +++ b/drivers/spi/spi-dw.h
> @@ -148,6 +148,7 @@ struct dw_spi {
>          unsigned long           paddr;
>          int                     irq;
>          u32                     fifo_len;       /* depth of the FIFO buffer */
> +       int                     dfs_off;        /* DFS field offset */
>          u32                     max_mem_freq;   /* max mem-ops bus freq */
>          u32                     max_freq;       /* max bus freq supported */
> 
> Then the only thing you'd need to add here is:
> -	/* CTRLR0[ 4/3: 0] Data Frame Size */
> -	cr0 |= (cfg->dfs - 1);
> +	/* CTRLR0[ 4/3: 0]/CTRLR0[ 20: 16] Data Frame Size */
> +	cr0 |= (cfg->dfs - 1) << dws->dfs_off;
> 
> * Note SPI core guarantees that bits_per_word is within the bits_per_word_mask
> * initialized in the SPI controller descriptor.
> 
>>   
>>   	if (!(dws->caps & DW_SPI_CAP_DWC_SSI))
>>   		/* CTRLR0[ 9:8] Transfer Mode */
>> @@ -828,6 +836,21 @@ static void spi_hw_init(struct device *dev, struct dw_spi *dws)
>>   		dev_dbg(dev, "Detected FIFO size: %u bytes\n", dws->fifo_len);
>>   	}
>>   
>> +	if (!(dws->caps & DW_SPI_CAP_DWC_SSI)) {
>> +		u32 cr0;
>> +
>> +		/*
>> +		 * Detect APB SSI CTRLR0 size by looking at the data
>> +		 * frame size field.
>> +		 */
> 
>> +		dw_writel(dws, DW_SPI_CTRLR0, 0xffffffff);
> 
> This isn't going to work because you need to disable the SSI controller
> first. Then please revert the change or cleanup the register and disable
> the controller back after finishing the detection.

In U-Boot at least, ctrlr0 is written before every transfer, so there is
no need to restore it afterward. Same for enr. I don't know whether this
holds true for Linux.

--Sean

> 
>> +		cr0 = dw_readl(dws, DW_SPI_CTRLR0);
> 
>> +		if (FIELD_GET(DWC_APB_CTRLR0_DFS32_MASK, cr0)) {
> 
> Instead of reading the DFS_32 field state I'd suggest to read the normal
> DFS bits as Sean does in the patch:
> https://patchwork.ozlabs.org/project/uboot/patch/20201016225755.302659-10-seanga2@gmail.com/
> 
> That'd be better because we can't guarantee what some older versions of
> the DW APB SSI controller preserve zeros in the upper part of CTRLR0, but
> we are sure the DFS field will always have zeros if DW APB SSI is
> synthesized with SSI_MAX_XFER_SIZE == 32.
> 
> So instead of having a new DWC_APB_CTRLR0_DFS32_MASK mask declared you'll
> need to add the macros as following:
> --- a/drivers/spi/spi-dw.h
> +++ b/drivers/spi/spi-dw.h
> @@ -41,6 +41,7 @@
>   
>   /* Bit fields in CTRLR0 */
>   #define SPI_DFS_OFFSET                 0
> +#define SPI_DFS_MASK                   GENMASK(3, 0)
> +#define SPI_DFS32_OFFSET		16
>   
>   #define SPI_FRF_OFFSET                 4
>   #define SPI_FRF_SPI                    0x0
> 
> The SPI_DFS32_OFFSET macro will be needed to initialize the dfs_off member
> if DFS32 capability is detected.
> 
>> +			dev_dbg(dev, "Detected 32-bits max data frame size\n");
> 
>> +			dws->caps |= DW_SPI_CAP_DWC_APB_XFER32;
> 
> I suggest to rename the flag to DW_SPI_CAP_DFS32, because it will be
> set for both DW APB SSI v4 (in fact for v3.23a and newer (see the Sean'
> patch log), but never mind) and DW SSI controllers. See the next comment
> for details of implementation.
> 
>> +		}
>> +	}
> 
> To sum up what I said above the detection procedure would look like this
> (note it's untested...):
> 
> +	/*
> +	 * Detect CTRLR0.DFS field size and offset by testing the lowest bits
> +	 * writability. Note DW SSI controller also has the extended DFS, but
> +	 * with zero offset.
> +	 */
> +	if (!(dws->caps & DW_SPI_CAP_DWC_SSI)) {
> +		u32 cr0, tmp = dw_readl(dws, DW_SPI_CTRLR0);
> +
> +		spi_enable_chip(dws, 0);
> +		dw_writel(dws, DW_SPI_CTRLR0, 0xffffffff);
> +		cr0 = dw_readl(dws, DW_SPI_CTRLR0);
> +		dw_writel(dws, DW_SPI_CTRLR0, tmp);
> +		spi_enable_chip(dws, 1);
> +		if (!(cr0 & SPI_DFS_MASK)) {
> +			dev_dbg(dev, "Detected 32-bits max data frame size\n");
> +			dws->caps |= DW_SPI_CAP_DFS32;
> *			dws->dfs_off = SPI_DFS32_OFFSET;
> +		}
> +	} else {
> +		dws->caps |= DW_SPI_CAP_DFS32;
> +	}
> 
> Note I've added the DW SSI fix here as it was suggested in a comment to
> your previous patchset revision...
> 
>> +
>>   	/* enable HW fixup for explicit CS deselect for Amazon's alpine chip */
>>   	if (dws->caps & DW_SPI_CAP_CS_OVERRIDE)
>>   		dw_writel(dws, DW_SPI_CS_OVERRIDE, 0xF);
>> @@ -864,7 +887,10 @@ 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;
>> -	master->bits_per_word_mask =  SPI_BPW_RANGE_MASK(4, 16);
> 
>> +	if (dws->caps & DW_SPI_CAP_DWC_APB_XFER32)
> 
> Please use the DW_SPI_CAP_DFS32 capability flag here.
> 
>> +		master->bits_per_word_mask = SPI_BPW_RANGE_MASK(4, 32);
>> +	else
>> +		master->bits_per_word_mask = SPI_BPW_RANGE_MASK(4, 16);
> 
> So this part of your fix will work for all types of controllers:
> - DW APB SSI v3.22a and older
> - DW APB SSI v3.23a and newer with SSI_MAX_XFER_SIZE == 16
> - DW APB SSI v3.23a and newer with SSI_MAX_XFER_SIZE == 32
> - DW SSI v1.*
> 
>>   	master->bus_num = dws->bus_num;
>>   	master->num_chipselect = dws->num_cs;
>>   	master->setup = dw_spi_setup;
>> diff --git a/drivers/spi/spi-dw.h b/drivers/spi/spi-dw.h
>> index faf40cb66498..cba5c1f8c456 100644
>> --- a/drivers/spi/spi-dw.h
>> +++ b/drivers/spi/spi-dw.h
>> @@ -9,6 +9,7 @@
>>   #include <linux/io.h>
>>   #include <linux/scatterlist.h>
>>   #include <linux/spi/spi-mem.h>
>> +#include <linux/bitfield.h>
>>   
>>   /* Register offsets */
>>   #define DW_SPI_CTRLR0			0x00
>> @@ -72,6 +73,12 @@
>>   #define DWC_SSI_CTRLR0_FRF_OFFSET	6
>>   #define DWC_SSI_CTRLR0_DFS_OFFSET	0
>>
>   
>> +/*
>> + * Data frame size bits mask in CTRLR0 for DWC_apb_ssi v4 when the
>> + * controller capability supports DW_SPI_CAP_DWC_APB_XFER32.
>> + */
> 
>> +#define DWC_APB_CTRLR0_DFS32_MASK	GENMASK(20, 16)
> 
> This won't be needed if you implement the fix as I suggest.
> 
>> +
>>   /*
>>    * For Keem Bay, CTRLR0[31] is used to select controller mode.
>>    * 0: SSI is slave
>> @@ -121,6 +128,7 @@ enum dw_ssi_type {
>>   #define DW_SPI_CAP_CS_OVERRIDE		BIT(0)
>>   #define DW_SPI_CAP_KEEMBAY_MST		BIT(1)
>>   #define DW_SPI_CAP_DWC_SSI		BIT(2)
> 
>> +#define DW_SPI_CAP_DWC_APB_XFER32	BIT(3)
> 
> Please replace it with DW_SPI_CAP_DFS32, since the capability flag
> will be used for the DW APB SSI v3.23a and newer and DW SSI controllers.
> 
> -Sergey
> 
>>   
>>   /* Slave spi_transfer/spi_mem_op related */
>>   struct dw_spi_cfg {
>> -- 
>> 2.28.0
>>