linux-kernel - Re: [PATCH v3 06/10] mtd: brcmstb

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Date:	Thu, 7 May 2015 11:48:38 -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 5/7/2015 11:42 AM, Brian Norris wrote:
> On Thu, May 07, 2015 at 12:01:02PM +0200, Arnd Bergmann wrote:
>> On Wednesday 06 May 2015 13:49:10 Brian Norris wrote:
>>> On Wed, May 06, 2015 at 09:12:43PM +0200, Arnd Bergmann wrote:
>>>> On Wednesday 06 May 2015 10:59:50 Brian Norris wrote:
>>>>> +       /*
>>>>> +        * Some SoCs integrate this controller (e.g., its interrupt bits) in
>>>>> +        * interesting ways
>>>>> +        */
>>>>> +       if (of_property_read_bool(dn, "brcm,nand-soc")) {
>>>>> +               struct device_node *soc_dn;
>>>>> +
>>>>> +               soc_dn = of_parse_phandle(dn, "brcm,nand-soc", 0);
>>>>> +               if (!soc_dn)
>>>>> +                       return -ENODEV;
>>>>> +
>>>>> +               ctrl->soc = devm_brcmnand_probe_soc(dev, soc_dn);
>>>>> +               if (!ctrl->soc) {
>>>>> +                       dev_err(dev, "could not probe SoC data\n");
>>>>> +                       of_node_put(soc_dn);
>>>>> +                       return -ENODEV;
>>>>> +               }
>>>>> +
>>>>> +               ret = devm_request_irq(dev, ctrl->irq, brcmnand_irq, 0,
>>>>> +                                      DRV_NAME, ctrl);
>>>>> +
>>>>> +               /* Enable interrupt */
>>>>> +               ctrl->soc->ctlrdy_set_enabled(ctrl->soc, true);
>>>>> +
>>>>> +               of_node_put(soc_dn);
>>>>> +       } else {
>>>>> +               /* Use standard interrupt infrastructure */
>>>>> +               ret = devm_request_irq(dev, ctrl->irq, brcmnand_ctlrdy_irq, 0,
>>>>> +                                      DRV_NAME, ctrl);
>>>>> +       }
>>>>>
>>>>
>>>> It looks to me like this should be handled as a nested irqchip, so the node
>>>> you look up gets used as the "interrupt-parent" instead, making the behavior
>>>> of this SoC transparent to the nand driver.
>>>
>>> You snipped the rest of the patch, which involves more than just IRQ
>>> handling. The same registers touch both interrupts and data bus endian
>>> configuration, so it can't possibly be done transparently to the NAND
>>> driver.
>>
>> Anything else in there?
> 
> Looks like miscellaneous NAND-related control bits. AXI and APB endian
> configuration; several interrupt-enable bits (we only use one for now);
> a clock-enable; and some timing test mode bits.
> 
>> The bus configuration would just involve writing
>> a constant value in some register, right?
> 
> I'm not an expert on the Cygnus/iProc chips, but I believe the answer is
> no: we *must* reconfigure the bus before and after each data
> transaction, because it affects the rest of the core too. Others on the
> CC list can probably elaborate.
> 

Yes, we must configure the bus before the after each data/cache
registers access, because it changes the APB bus endianess.

Thanks,

Ray
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