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

Sean Anderson
2020-11-09T14:35:46Z

On 11/9/20 9:33 AM, Sean Anderson wrote:
> On 11/9/20 9:25 AM, Serge Semin 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@intel.com/
>> it has been ok to use the lowest four bits for DFS setting. Is the commit
>> message misleading there?
>
> This commit message is a truncated version of [1]. Importantly, DFS is
> valid when SSI_MAX_XFER_SIZE=16. When it =32, then DFS_32 must be used
> (since DFS is constant 0xF). Since SSI_MAX_XFER_SIZE is a synthesis
s/0xF/0x0/

> parameter, there exist devices where DFS must be used, and also where
> DFS_32 must be used.
>
> [1] https://patchwork.ozlabs.org/project/uboot/patch/20201016225755.302659-10-seanga2@gmail.com/
>
> --Sean
>
>>
>>> Introduce the DW SPI capability flag DW_SPI_CAP_DFS_32 to let a
>>> platform signal that this layout is in use. Modify
>>> dw_spi_update_config() to test this capability flag to set the data
>>> frame format field at the correct register location.
>>>
>>> Suggested-by: Sean Anderson <seanga2@gmail.com>
>>> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
>>> ---
>>> drivers/spi/spi-dw-core.c | 8 ++++++--
>>> drivers/spi/spi-dw.h | 9 +++++++++
>>> 2 files changed, 15 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/spi/spi-dw-core.c b/drivers/spi/spi-dw-core.c
>>> index 2e50cc0a9291..841c85247f01 100644
>>> --- a/drivers/spi/spi-dw-core.c
>>> +++ b/drivers/spi/spi-dw-core.c
>>> @@ -311,8 +311,12 @@ 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_DFS_32))
>>> + /* CTRLR0[ 4/3: 0] Data Frame Size */
>>> + cr0 |= (cfg->dfs - 1);
>>> + else
>>> + /* CTRLR0[20: 16] Data Frame Size */
>>> + cr0 |= (cfg->dfs - 1) << DWC_APB_CTRLR0_32_DFS_OFFSET;
>>
>> If you extend the dfs field from four to five bits, then
>> controller->bits_per_word_mask field should be properly updated too.
>>
>> Alas it hasn't been done for the DWC_ssi version of the core. So I suppose it
>> should be fixed for the both of them.
>>
>> Just for the record. There are very handy macros for setting and getting bit fields
>> to/from a variable. This is a good place to use them instead of manually
>> shifting and defining the offsets. The macros are defined in linux/bitfield.h .
>> Alas this driver hasn't been converted to using them. So I won't insist on using
>> them here. But I hope someone will fix it sometime in future...
>
> I second that request.
>
>> -Sergey
>>
>>>
>>> if (!(dws->caps & DW_SPI_CAP_DWC_SSI))
>>> /* CTRLR0[ 9:8] Transfer Mode */
>>> diff --git a/drivers/spi/spi-dw.h b/drivers/spi/spi-dw.h
>>> index faf40cb66498..48a11a51a407 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 +73,13 @@
>>> #define DWC_SSI_CTRLR0_FRF_OFFSET 6
>>> #define DWC_SSI_CTRLR0_DFS_OFFSET 0
>>>
>>> +/*
>>> + * Bit fields in CTRLR0 for DWC_apb_ssi v4 32-bits ctrlr0.
>>> + * Based on DW_apb_ssi Databook v4.02a.
>>> + */
>>> +#define DWC_APB_CTRLR0_32_DFS_OFFSET 16
>>> +#define DWC_APB_CTRLR0_32_DFS_MASK GENMASK(20, 16)
>>> +
>>> /*
>>> * For Keem Bay, CTRLR0[31] is used to select controller mode.
>>> * 0: SSI is slave
>>> @@ -121,6 +129,7 @@ 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_DFS_32 BIT(3)
>>>
>>> /* Slave spi_transfer/spi_mem_op related */
>>> struct dw_spi_cfg {
>>> --
>>> 2.28.0
>>>
>