Groups > linux.kernel > #1200198

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

From	"R, Vignesh" <vigneshr@ti.com>
Newsgroups	linux.kernel
Subject	Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read
Date	2015-08-04 20:10 +0200
Message-ID	<pTOP0-1jD-9@gated-at.bofh.it> (permalink)
References	<pR8Kd-43p-3@gated-at.bofh.it> <pR8Ke-43p-33@gated-at.bofh.it> <pSq2n-17l-27@gated-at.bofh.it> <pTg0V-PQ-1@gated-at.bofh.it> <pTMNc-6DQ-3@gated-at.bofh.it>
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On 8/4/2015 9:21 PM, Mark Brown wrote:
> On Mon, Aug 03, 2015 at 10:27:19AM +0530, Vignesh R wrote:
> 
>> @use_mmap_mode: Some SPI controller chips are optimized for interacting
>> with serial flash memories. These chips have memory mapped interface,
>> through which entire serial flash memory slave can be read/written as if
>> though they are physical memories (like RAM). Using this interface,
>> flash can be accessed using memcpy() function and the spi controller
>> hardware will take care of communicating with serial flash over SPI.
>> Setting this flag will indicate the SPI controller driver that the
>> spi_message is from mtd layer to read from/write to flash. The SPI
>> master driver can then appropriately switch the controller to memory
>> mapped interface to read from/write to flash, based on this flag (See
>> drivers/spi/spi-ti-qspi.c for example).
>> NOTE: If the SPI controller chip lacks memory mapped interface, then the
>> driver will ignore this flag and use normal SPI protocol to read
>> from/write to flash. Communication with non-flash SPI devices is not
>> possible using the memory mapped interface.
> 
> I still can't tell from the above what this interface is supposed to do.
> It sounds like the use of memory mapped mode is supposed to be
> transparent to users, it should just affect how the controller interacts
> with the hardware, but if that's the case why do we need to expose it to
> users at all?  Shouldn't the driver just use memory mapped mode if it's
> faster?
> 

TI QSPI controller has two blocks:
1. SPI_CORE: This is generic(normal) spi mode. This can be used to
communicate with any SPI devices (serial flashes as well as non-flash
devices like touchscreen).
2. SFI_MM_IF(SPI memory mapped interface): The SFI_MM_IF block only
allows reading and writing to an SPI flash device only. Used to speed up
flash reads. It _cannot_ be used to communicate with non flash devices.
Now, the spi_message that ti-qspi receives in transfer_one() callback
can be from mtd device(in which case SFI_MM_IF can be used) or from any
other non flash SPI device (in which case SFI_MM_IF must not be used
instead SPI_CORE is to be used) but there is no way(is there?) to
distinguish where spi_message is from. Therefore I introduced flag
(use_mmap_mode) to struct spi_message. mtd driver will set flag to true,
this helps the ti-qspi driver to determine that the user is flash device
and thus can do read via SFI_MM_IF. If this flag is not set then the
user is assumed to be non flash SPI driver and will use SPI_CORE block
to communicate.

On the whole, I just need a way to determine that the user is a flash
device in order to switch to memory mapped interface.

Regards
Vignesh
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Thread

[RFC PATCH 0/5] Add memory mapped read support for TI QSPI. Vignesh R <vigneshr@ti.com> - 2015-07-28 10:50 +0200
  [RFC PATCH 4/5] ARM: dts: DRA7: Add memory map region entries for qspi Vignesh R <vigneshr@ti.com> - 2015-07-28 10:50 +0200
    Re: [RFC PATCH 4/5] ARM: dts: DRA7: Add memory map region entries  for qspi Vignesh R <vigneshr@ti.com> - 2015-08-03 07:10 +0200
      Re: [RFC PATCH 4/5] ARM: dts: DRA7: Add memory map region entries  for qspi Mark Brown <broonie@kernel.org> - 2015-08-04 18:00 +0200
    Re: [RFC PATCH 4/5] ARM: dts: DRA7: Add memory map region entries  for qspi Vignesh R <vigneshr@ti.com> - 2015-08-03 07:10 +0200
    Re: [RFC PATCH 4/5] ARM: dts: DRA7: Add memory map region entries  for qspi Vignesh R <vigneshr@ti.com> - 2015-08-03 07:20 +0200
  [RFC PATCH 2/5] spi: spi-ti-qspi: Add memory mapped read support Vignesh R <vigneshr@ti.com> - 2015-07-28 10:50 +0200
  [RFC PATCH 1/5] spi: introduce flag for memory mapped read Vignesh R <vigneshr@ti.com> - 2015-07-28 10:50 +0200
    Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Vignesh R <vigneshr@ti.com> - 2015-08-03 07:00 +0200
      Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Mark Brown <broonie@kernel.org> - 2015-08-04 18:00 +0200
        Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read "R, Vignesh" <vigneshr@ti.com> - 2015-08-04 20:10 +0200
          Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Michal Suchanek <hramrach@gmail.com> - 2015-08-05 07:30 +0200
            Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Vignesh R <vigneshr@ti.com> - 2015-08-05 07:40 +0200
              Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Michal Suchanek <hramrach@gmail.com> - 2015-08-05 08:00 +0200
          Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Mark Brown <broonie@kernel.org> - 2015-08-05 14:00 +0200
            Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Michal Suchanek <hramrach@gmail.com> - 2015-08-05 14:50 +0200
              Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Mark Brown <broonie@kernel.org> - 2015-08-05 14:50 +0200
                Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Michal Suchanek <hramrach@gmail.com> - 2015-08-05 15:00 +0200
                Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Mark Brown <broonie@kernel.org> - 2015-08-06 11:10 +0200
                Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Michal Suchanek <hramrach@gmail.com> - 2015-08-06 12:10 +0200
                Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-08-06 12:30 +0200
                Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Mark Brown <broonie@kernel.org> - 2015-08-06 13:10 +0200
                Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Michal Suchanek <hramrach@gmail.com> - 2015-08-06 13:10 +0200
                Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Vignesh R <vigneshr@ti.com> - 2015-08-06 14:30 +0200
                Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-08-06 16:00 +0200
                Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Geert Uytterhoeven <geert@linux-m68k.org> - 2015-08-06 18:20 +0200
                Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Michal Suchanek <hramrach@gmail.com> - 2015-08-06 20:30 +0200
                Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-08-06 23:40 +0200
                Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Michal Suchanek <hramrach@gmail.com> - 2015-08-07 09:40 +0200
                Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Vignesh R <vigneshr@ti.com> - 2015-08-07 10:40 +0200
                Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Martin Sperl <martin@sperl.org> - 2015-08-07 10:30 +0200
                Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Michal Suchanek <hramrach@gmail.com> - 2015-08-07 12:20 +0200
                Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Vignesh R <vigneshr@ti.com> - 2015-08-12 11:30 +0200
                Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Mark Brown <broonie@kernel.org> - 2015-08-06 18:50 +0200
                Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Mark Brown <broonie@kernel.org> - 2015-08-06 20:30 +0200
                Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Mark Brown <broonie@kernel.org> - 2015-08-06 13:30 +0200
                Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Michal Suchanek <hramrach@gmail.com> - 2015-08-06 13:50 +0200
                Re: [RFC PATCH 1/5] spi: introduce flag for memory mapped read Mark Brown <broonie@kernel.org> - 2015-08-06 18:10 +0200
  [RFC PATCH 5/5] ARM: dts: AM4372: Add memory map region entries for qspi Vignesh R <vigneshr@ti.com> - 2015-07-28 10:50 +0200
  [RFC PATCH 3/5] mtd: devices: m25p80: set flag to request memory mapped read Vignesh R <vigneshr@ti.com> - 2015-07-28 10:50 +0200

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