linux-kernel - Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read

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Date:	Fri, 7 Aug 2015 14:05:10 +0530
From:	Vignesh R <vigneshr@...com>
To:	Michal Suchanek <hramrach@...il.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Mark Brown <broonie@...nel.org>,
	devicetree <devicetree@...r.kernel.org>,
	Brian Norris <computersforpeace@...il.com>,
	Tony Lindgren <tony@...mide.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-spi <linux-spi@...r.kernel.org>,
	Huang Shijie <b32955@...escale.com>,
	MTD Maling List <linux-mtd@...ts.infradead.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	David Woodhouse <dwmw2@...radead.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read



On 08/07/2015 01:08 PM, Michal Suchanek wrote:

> Now since the description is clearer it's obvious that ti-qspi cannot
> work fully mmapped as fsl-qspi does because the setup has to be done
> over normal spi access and using non-m25p80 devices on the same bus is
> a requirement.
> 
> The place where it is known if a transfer can use the mmap access is m25p80.c
> 
> So my suggestion is
> 
>  - add a new method for spi master that gets the read opcode, dummy
> length, address, address length, buffer, buffer length and performs
> read from the flash memory in a hardware-specific way
> 
> - add a check in m25p80.c that the master supports this feature and if
> so use it (eg check that the method is non-null)
> 
> Presumably if some new SPI controllers with similar feature are
> supported in the future they can use the same inteface because you
> pass on everything the m25p80 read knows.
> 

Ok... Do you mean something like this?

I will take m25p80 as example but can be expanded for any flash.

In include/linux/mtd.h:
	struct spi_mtd_config_info {
		struct spi_device 	*spi;
	        u32                     page_size;
	        u8                      addr_width;
       		u8                      erase_opcode;
	        u8                      read_opcode;
        	u8                      read_dummy;
	        u8                      program_opcode;
        	enum read_mode          flash_read;

	} /* subset of struct spi_nor */


In m25p80.c:

	static int m25p80_read(struct spi_nor *nor, loff_t from,
				size_t len, size_t *retlen,
				u_char *buf)
	{
		struct spi_mtd_config_info info;
		struct spi_device *spi;
		
		if (spi->master->spi_mtd_mmap_read) {
		  /* Populate spi_mtd_config_info */
		  spi->master->spi_mtd_mmap_read(&info, from, len,
						 retlen, buf);
		}
		else {
		/* no mtd specific acceleration supported try normal
		 * SPI way of communicating with flash
		 * continue with current code
		 * set up spi_message and call spi_sync()
		 */
	}

      }

In spi-ti-qspi.c:
Implement spi_mtd_mmap_read while holding master->bus_lock mutex.


-- 
Regards
Vignesh
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