Date:	Fri, 8 May 2015 14:58:31 -0700
From:	Ray Jui <rjui@...adcom.com>
To:	Brian Norris <computersforpeace@...il.com>,
	Arnd Bergmann <arnd@...db.de>
CC:	<linux-mtd@...ts.infradead.org>, Dmitry Torokhov <dtor@...gle.com>,
	Anatol Pomazao <anatol@...gle.com>,
	Corneliu Doban <cdoban@...adcom.com>,
	Jonathan Richardson <jonathar@...adcom.com>,
	Scott Branden <sbranden@...adcom.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Rafał Miłecki <zajec5@...il.com>,
	<bcm-kernel-feedback-list@...adcom.com>,
	Dan Ehrenberg <dehrenberg@...omium.org>,
	Gregory Fong <gregory.0xf0@...il.com>,
	<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Kevin Cernekee <cernekee@...il.com>
Subject: Re: [PATCH v3 06/10] mtd: brcmstb_nand: add SoC-specific support



On 5/8/2015 1:47 PM, Brian Norris wrote:
> On Fri, May 08, 2015 at 09:49:02PM +0200, Arnd Bergmann wrote:
>> On Friday 08 May 2015 12:38:50 Brian Norris wrote:
>>> On Fri, May 08, 2015 at 03:41:10PM +0200, Arnd Bergmann wrote:
> [...]
> 
>>> To be clear, since I'm not sure if you're confused below:
>>>
>>>  * Cygnus is a family of chips using the IPROC architecture, coming from
>>>    the Infrastructure/Networking Group; there are BCMxxxx numbers noted
>>>    in arch/arm/mach-bcm/Kconfig for them, but I usually just refer to
>>>    the Cygnus family or the IPROC architecture.
>>>
>>>  * BCM63xxx is a class of DSL chips from the Broadband/Connectivity
>>>    Group.
>>
>> Thanks for the clarification, I think that is roughly what I thought it was,
>> but I'm still not sure about brcmstb. Is that related to bcm63xxx or separate?
> 
> I think arch/arm/mach-bcm/Kconfig has the best summary. brcmstb is
> separate; BCM7xxx is generally (always?) Set-Top Box.
> 
> Another potentially confusing point: the main driver is named
> 'brcsmtb_nand' since the NAND core (and driver) originated from STB
> chips. But that core was applied to other non-STB chips, and so the
> driver has been extended.
> 
>>>> bcm63138_nand_driver with its own probe() function that calls the
>>>> common probe function. That would make the soc specific parts
>>>> better contained and match how we normally do abstractions of
>>>> similar drivers.
>>>
>>> OK, so I can imagine this might require changing the DT binding a bit [1]
>>> (is that your goal?). But what's the intended software difference? [2]
>>> I'll still be passing around the same sorts of callbacks from the
>>> 'iproc_nand' probe to the common probe function.
> 
> ^^ before getting bogged down on the DT details (which can be changed
> independently), I'd like to address this point.
> 
>>> Brian
>>>
>>> [1] e.g.:
>>>
>>>        nand: nand@...46000 {
>>>                compatible = "brcm,iproc-nand", "brcm,brcmnand-v6.1", "brcm,brcmnand";
>>>                reg = <0x18046000 0x600>, <0xf8105408 0x600>, <0x18046f00 0x20>;
>>>                reg-names = "nand", "iproc-idm", "iproc-ext";
>>>                interrupts = <GIC_SPI 69 IRQ_TYPE_LEVEL_HIGH>;
>>>
>>>                #address-cells = <1>;
>>>                #size-cells = <0>;
>>>
>>>                brcm,nand-has-wp;
>>>        };
>>>
>>> This captures the extra "iproc-*" register ranges. Then we could have
>>> the iproc_nand driver bind against "brcm,iproc-nand", then call into the
>>> common probe, which would then accept/reject based on
>>> "brcm,brcmnand-vX.Y".
>>>
>>> [2] The DT structure from [1] could actually accommodate either driver
>>> structure just fine. So maybe that means it's a better hardware
>>> description?
>>
>> Yes, I think this makes sense overall. Regarding the specific example, can you
>> clarify how the register areas in iproc are structured?
>>
>> The 0xf8105408 and 0x18046f00 start addresses are not aligned to large powers
>> of two, which often indicates that they are part of some other, larger,
>> unit that might need to have a driver of its own, so before we specify
>> a binding like the one you proposed above I'd like to make sure we're not
>> getting ourselves into trouble later.
> 
> I may want the Cygnus guys to speak up here, partly for technical
> expertise and partly to know how much they care to share...
> 
> <0xf8105408 0x600>: covers a series of NAND_IDM registers. NAND has a
> few bits we don't care about (for debugging, logging, and resetting), as
> well as its interrupt enable bits. The adjacent blocks cover similar IDM
> blocks for other cores (SPI, PNOR, DDR), and they are similarly
> unaligned. Not sure why, exactly; probably just a compact layout.

Yes, starting from 0xf8105408, within the range of 0x600, there are
various NAND_IDM registers scattered, which is indeed a very weird
register layout.

Like Brian said, most of those NAND_IDM registers are for debugging,
logging, or status reporting. As of today, we only care about the first
register, that contains a bunch of bits that allow you to configure the
endianness of the AXI/APB bus, enabling NAND interrupts and clocks.

> 
> <0x18046f00 0x20>: a series of 8 NAND interrupt registers, each word
> containing a single bit representing status/clear. There is nothing
> between the "nand" range and this range, and the SPI core register range
> follows.

Correct.

> 
> So I think these are pretty clearly-delineated register ranges for NAND,
> and the alignment is not really missing anything. Adjacent hardware
> (e.g., SPI) is independent, though pieces look similar. For one, it has
> similar:
> 
>  * interrupt enable bits in the IDM range (0xf8106408 to 0xf8106a00);
>    and
>  * interrupt status/clear following the SPI block (0x180473a0 to
>    0x180473b8)
> 
> Brian
> 
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