netdev - Re: [RFT][PATCH V2 09/10] net: dsa: microchip: Factor out regmap config generation into common header

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Date:   Wed, 9 Jan 2019 22:59:42 +0100
From:   Marek Vasut <marex@...x.de>
To:     Tristram.Ha@...rochip.com
Cc:     f.fainelli@...il.com, andrew@...n.ch, Woojung.Huh@...rochip.com,
        netdev@...r.kernel.org, UNGLinuxDriver@...rochip.com
Subject: Re: [RFT][PATCH V2 09/10] net: dsa: microchip: Factor out regmap
 config generation into common header

On 1/9/19 8:58 PM, Tristram.Ha@...rochip.com wrote:
>> This is the regmap_config I used in Linux 4.9:
>>
>> 	.reg_bits		= SPI_REGMAP_REG,
>> 	.val_bits		= SPI_REGMAP_VAL,
>> 	.pad_bits		= SPI_REGMAP_PAD,
>> 	.read_flag_mask	= KS_SPIOP_RD << SPI_REGMAP_MASK_S,
>> 	.write_flag_mask	= KS_SPIOP_WR << SPI_REGMAP_MASK_S,
>> 	.reg_format_endian	= REGMAP_ENDIAN_BIG,
>> 	.val_format_endian	= REGMAP_ENDIAN_BIG,
>>
>> For KSZ9477:
>>
>> SPI_CMD_LEN		4
>> SPI_REGMAP_PAD	SPI_TURNAROUND_SHIFT
>> SPI_REGMAP_VAL	8
>> SPI_REGMAP_REG	\
>> 	(SPI_CMD_LEN * SPI_REGMAP_VAL - SPI_TURNAROUND_SHIFT)
>> SPI_REGMAP_MASK_S	\
>> 	(SPI_ADDR_SHIFT + SPI_TURNAROUND_SHIFT - \
>> 	(SPI_CMD_LEN * SPI_REGMAP_VAL - 8))
>>
>> For KSZ8795:
>>
>> SPI_CMD_LEN		2
>> SPI_REGMAP_PAD	SPI_TURNAROUND_S
>> SPI_REGMAP_VAL	8
>> SPI_REGMAP_REG	\
>> 	(SPI_CMD_LEN * SPI_REGMAP_VAL - SPI_TURNAROUND_S)
>> SPI_REGMAP_MASK_S	\
>> 	(SPI_ADDR_S + SPI_TURNAROUND_S - \
>> 	(SPI_CMD_LEN * SPI_REGMAP_VAL - 8))
>>
>> So the differences between KSZ9477 and KSZ8795 are SPI_CMD_LEN,
>> SPI_ADDR_S, and SPI_TURNAROUND_S.
>>
>> KSZ9477:
>>
>> .reg_bits = 32 - 5 = 27
>> .val_bits = 8
>> .pad_bits = 5
>> .read_flag_mask = KS_SPIOP_RD << 5,
>>
>> KSZ8795:
>>
>> .reg_bits = 16 - 1 = 15
>> .val_bits = 8
>> .pad_bits = 1
>> .read_flag_mask = KS_SPIOP_RD << 5,
>>
>> The regmap.c code uses reg_bits + reg_shift (which comes from pad_bits) to
>> decide whether the register space is 16-bit or 32-bit.  The value space is
>> always 8-bit.
>>
>> The shift for _flag_mask turns out to be the same for both KSZ9477 and
>> KSZ8795.
> 
> I just looked at your regmap code and you use 3 regmap pointers for specific 8-bit, 16-bit, and 32-bit accesses.  The switch access is always 8-bit.  It has automatic register increment so that you can access arbitrary length of registers.  The use of 16-bit and 32-bit accesses makes access efficient if it makes sense.

Right, that's what happens here.

> Most older switches define registers in 8-bit.  Exceptions are the default VID and indirect access.
> 
> A specific switch mostly defines registers in 16-bit because it shares the core design with an Ethernet controller.
> 
> KSZ9477 is the newer designed switch and it gets some designs from older switches and that is why it has a mix of 8-bit, 16-bit, and 32-bit register definitions.

Right, that's quite horrible.

> In my code I just use regmap_bulk_read and regmap_bulk_write and still use the old spi access functions for specific 8-bit, 16-bit, and 32-bit accesses.

Let's not mix regmap and non-regmap accesses, that'd be a mess. Let's
stick to one, regmap.

> We can combine the logic of ksz_spi_read8 and others into ksz_read8 and so they can be used for both SPI and I2C accesses.

You can just use regmap_*() accessors and regmap will deal with i2c/spi
abstraction for you, that's the idea.

-- 
Best regards,
Marek Vasut