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

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Date:	Wed, 12 Aug 2015 14:57:03 +0530
From:	Vignesh R <vigneshr@...com>
To:	Michal Suchanek <hramrach@...il.com>,
	Martin Sperl <martin@...rl.org>
CC:	Russell King - ARM Linux <linux@....linux.org.uk>,
	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>,
	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 03:46 PM, Michal Suchanek wrote:
[snip]
> On 7 August 2015 at 10:35, Vignesh R <vigneshr@...com> wrote:
>>
>>
>> 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 */
>>
> 
> I would just pass these as separate arguments to the function but whatver.
> 
>> 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.
>>
> 

I will re-submit patches based on the above idea, if there are no
further comments..

-- 
Thanks
Vignesh
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