linux-kernel - Re: [PATCH v4 4/5] ARM: dts: DRA7: add entry for qspi mmap region

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Date:	Tue, 1 Dec 2015 08:39:50 -0800
From:	Tony Lindgren <tony@...mide.com>
To:	Vignesh R <vigneshr@...com>
Cc:	Brian Norris <computersforpeace@...il.com>,
	Mark Brown <broonie@...nel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Russell King <linux@....linux.org.uk>, hramrach@...il.com,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-mtd@...ts.infradead.org, linux-spi@...r.kernel.org
Subject: Re: [PATCH v4 4/5] ARM: dts: DRA7: add entry for qspi mmap region

* Vignesh R <vigneshr@...com> [151130 20:46]:
> On 12/01/2015 04:04 AM, Tony Lindgren wrote:
> > 
> > Actually none of the IO areas above are within the same interconnect target:
> > 
> > 0x4b300000  QSPI0 address space in L3 main interconnect
> > 0x5c000000  QSPI1 address space in L3 main interconnect
> 
> 
> First address range (configuration port: 0x4b300000) corresponds to QSPI
> registers space. These registers alone are sufficient for generic SPI
> communication (serial flash as well as non-flash SPI devices).

OK

> In order to speed up SPI flash reads SFI_MM_IF(SPI memory mapped
> interface) is provided by QSPI IP. This _cannot_ be used with non-flash
> devices.

OK

> The second address range (0x5c000000) corresponds to memory-mapped
> region of SFI_MM_IF, through which SPI flash memories can be read as if
> though they were RAM addresses (i.e using readl/memcpy). The SFI_MM_IF
> block that takes care of communicating over SPI bus and getting the data
> from flash device.

OK

> But SFI_MM_IF block needs to know some flash specific information(such
> as read opcode, address bytes, dummy bytes, mode). This information must
> first be populated in QSPI_SPI_SETUP*_REG(0x4B300054-60) before
> accessing SFI_MM_IF address range via readl.
> Both addresses space belong to same instance of the driver, one
> corresponds to register space and other is memory-mapped region.
> Therefore both regions are claimed by the same driver.

OK

> > 0x4a002558  CTRL_CORE_CONTROL_IO_2 in System Control Module (SCM) in L4_CFG
> > 
> > The first two address spaces should be two separate instances of this driver.
> 
> Not actually two instances.

OK. They are both on L3 main so that won't cause any issues for separate
interconnect driver instances. As they are still separate targets flushing
a posted write to one area will not flush anything to the other.

> > The CTRL_CORE_CONTROL_IO_2 needs seems like a shared clock register that
> > needs to be accessed using the clock framework most likely.
> > 
> 
> Not shared clock.
> The CTRL_CORE_CONTROL_IO_2[10:8] QSPI_MEMMAPPED_CS bit fields provides a
> functionality for remapping the previously described address space which
> starts at 0x5C000000 L3_MAIN address to one of the four supported chip
> selects.
> How about using syscon to access CTRL_CORE_CONTROL_IO_2?

A separate driver implementing some Linux generic framework would be idael :)

But if that does not fit, yeah then syscon makes sense as that IO range
will be on separate interconnect driver (and clock and possibly power domain)
instances eventually.

Regards,

Tony

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