linux-kernel - Re: [PATCH v3 1/5] spi: introduce mmap read support for spi flash devices

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Message-ID: <56441678.6040504@ti.com>
Date:	Thu, 12 Nov 2015 10:02:56 +0530
From:	Vignesh R <vigneshr@...com>
To:	Brian Norris <computersforpeace@...il.com>
CC:	Mark Brown <broonie@...nel.org>, Tony Lindgren <tony@...mide.com>,
	Rob Herring <robh@...nel.org>,
	Michal Suchanek <hramrach@...il.com>,
	Russell King <linux@....linux.org.uk>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, Marek Vasut <marex@...x.de>
Subject: Re: [PATCH v3 1/5] spi: introduce mmap read support for spi flash
 devices

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
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