Subject: [PATCH v3 1/5] spi: introduce mmap read support for spi flash devices

From: [email-masked] (Vignesh R)
Date: Thu, 12 Nov 2015 10:02:56 +0530

Hi Brian,

On 11/12/2015 12:54 AM, Brian Norris wrote:
> In addition to my other comments:
> 

[...]

>> +	int (*spi_mtd_mmap_read)(struct  spi_device *spi,
>> +				 loff_t from, size_t len,
>> +				 size_t *retlen, u_char *buf,
>> +				 u8 read_opcode, u8 addr_width,
>> +				 u8 dummy_bytes);
> 
> This is seeming to be a longer and longer list of arguments. I know MTD
> has a bad habit of long argument lists (which then cause a ton of
> unnecessary churn when things need changed in the API), but perhaps we
> can limit the damage to the SPI layer. Perhaps this deserves a struct to
> encapsulate all the flash read arguments? Like:
> 
> struct spi_flash_read_message {
> 	loff_t from;
> 	size_t len;
> 	size_t *retlen;
> 	void *buf;
> 	u8 read_opcode;
> 	u8 addr_width;
> 	u8 dummy_bits;
> 	// additional fields to describe rx_nbits for opcode/addr/data
> };
> 
> struct spi_master {
> 	...
> 	int (*spi_flash_read)(struct spi_device *spi,
> 			      struct spi_flash_message *msg);
> };

Yeah.. I think struct encapsulation helps, this can also be used to pass
sg lists for dma in future. I will rework the series with your
suggestion to include nbits for opcode/addr/data.
Also, will add validation logic (similar to __spi_validate()) to check
whether master supports dual/quad mode for opcode/addr/data. I am
planning to add this validation code to spi_flash_read_validate(in place
of spi_mmap_read_supported())
Thanks!

-- 
Regards
Vignesh