linux-kernel - Re: [PATCH 3/3] mtd: spi-nor: Altera Quadspi Flash Controller v2 Platform driver

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Message-ID: <alpine.DEB.2.20.1706271028260.8058@mgerlach-VirtualBox>
Date:   Tue, 27 Jun 2017 10:38:44 -0700 (PDT)
From:   matthew.gerlach@...ux.intel.com
To:     Marek Vasut <marek.vasut@...il.com>
cc:     vndao@...era.com, dwmw2@...radead.org, computersforpeace@...il.com,
        boris.brezillon@...e-electrons.com, richard@....at,
        cyrille.pitchen@...ev4u.fr, robh+dt@...nel.org,
        mark.rutland@....com, linux-mtd@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        gregkh@...uxfoundation.org, davem@...emloft.net, mchehab@...nel.org
Subject: Re: [PATCH 3/3] mtd: spi-nor: Altera Quadspi Flash Controller v2
 Platform driver



On Tue, 27 Jun 2017, Marek Vasut wrote:

> On 06/27/2017 05:15 PM, matthew.gerlach@...ux.intel.com wrote:
>>
>>
>> On Tue, 27 Jun 2017, Marek Vasut wrote:
>>
>>> On 06/26/2017 06:13 PM, matthew.gerlach@...ux.intel.com wrote:
>>>> From: Matthew Gerlach <matthew.gerlach@...ux.intel.com>
>>>
>>> Just wrap it into the Altera QSPI driver , no need for separate platform
>>> driver IMO.
>>
>> Hi Marek,
>>
>> I answered this question when you asked why the header file was
>> necessary, but I think further discussion could be helpful, since this
>> problem is becoming more prevelent.  The Altera Quadspi component is a
>> soft IP in a
>> FPGA, and the processor using the component may or may not have device
>> tree support compiled into the Linux kernel.  Since device tree support
>> may or may not be available, the device tree specific code must be
>> separated
>> from the core driver code.
>
> I see, that's fine, although there is no PCIe or other support in this
> submission. Is that planned ?

You probably would not see a PCIe driver for a card with a FPGA that would 
only have the Altera Quadspi component on it.  Usually a FPGA has several 
components, each requiring their own driver which are considered 
sub-drivers of the PCIe driver.  I will be adding Altera Quadspi support 
to the Intel-FPGA PCIe driver that is currently under review.  We have 
also seen people use the Altera Quadspi with a NIOS-II soft processor, and 
I expect someone would want to use the component with ARM SOCFPGAs.

Matthew Gerlach

>
>> One can certainly make the case, that device tree support could/should
>> be available everywhere, but the current reality is most x86 Linux
>> kernel configurations do not include device tree support.
>>
>> For the record, I believe device trees, and more specifically device
>> tree overlays, are the best way for Linux to use FPGAs, but I have to
>> deal with the current realities.
>>
>> Thanks again for all the great feedback.
>>
>> Matthew Gerlach
>
> [...]
>
> -- 
> Best regards,
> Marek Vasut
>