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 10:15:26 +0530
From:	Vignesh R <vigneshr@...com>
To:	Tony Lindgren <tony@...mide.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

On 12/01/2015 04:04 AM, Tony Lindgren wrote:
> * Vignesh R <vigneshr@...com> [151129 21:16]:
>> Add qspi memory mapped region entries for DRA7xx based SoCs. Also,
>> update the binding documents for the controller to document this change.
>>
>> Acked-by: Rob Herring <robh@...nel.org>
>> Signed-off-by: Vignesh R <vigneshr@...com>
> ...
>> --- a/Documentation/devicetree/bindings/spi/ti_qspi.txt
>> +++ b/Documentation/devicetree/bindings/spi/ti_qspi.txt
>> @@ -26,3 +26,17 @@ qspi: qspi@...00000 {
>>  	spi-max-frequency = <25000000>;
>>  	ti,hwmods = "qspi";
>>  };
>> +
>> +For dra7xx:
>> +qspi: qspi@...00000 {
>> +	compatible = "ti,dra7xxx-qspi";
>> +	reg = <0x4b300000 0x100>,
>> +	      <0x5c000000 0x4000000>,
>> +	      <0x4a002558 0x4>;
>> +	reg-names = "qspi_base", "qspi_mmap",
>> +		    "qspi_ctrlmod";
>> +	#address-cells = <1>;
>> +	#size-cells = <0>;
>> +	spi-max-frequency = <48000000>;
>> +	ti,hwmods = "qspi";
>> +};
> 
> 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).

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.
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.
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.

> 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.

> 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?

-- 
Regards
Vignesh
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