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Subject: Re: [PATCH v4 2/2] PCI: Add tango PCIe host bridge support
To: Mason <slash.tmp@free.fr>
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Cc: Marc Gonzalez <marc_gonzalez@sigmadesigns.com>,
        Bjorn Helgaas <helgaas@kernel.org>,
        linux-pci <linux-pci@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Robin Murphy <robin.murphy@arm.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Liviu Dudau <liviu.dudau@arm.com>,
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        Linux ARM <linux-arm-kernel@lists.infradead.org>,
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        Phuong Nguyen <phuong_nguyen@sigmadesigns.com>,
        LKML <linux-kernel@vger.kernel.org>
From: Marc Zyngier <marc.zyngier@arm.com>
Organization: ARM Ltd
Message-ID: <276e40e8-6539-2765-7ce7-9a942b56d54d@arm.com>
Date: Thu, 25 May 2017 14:20:16 +0100
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On 25/05/17 13:41, Mason wrote:
> On 25/05/2017 14:23, Marc Zyngier wrote:
>> On 25/05/17 13:00, Mason wrote:
>>> On 25/05/2017 10:48, Marc Zyngier wrote:
>>>> Please have some defines for these magic values.
>>>
>>> Typical driver do
>>> #define MUX_OFFSET 0x48
>>> and then access the register's value through
>>> readl_relaxed(pcie->base + MUX_OFFSET);
>>>
>>> I can't do that because the registers were shuffled around
>>> between revision 1 and revision 2. Thus, instead of an
>>> explicitly-named macro (MUX_OFFSET), I used an explicitly-
>>> named field (pcie->mux) and access the register's value
>>> through readl_relaxed(pcie->mux);
>>
>> That doesn't prevent you from having a TANGO_V1_MUX_OFFSET define, which
>> you can supplement with a V2 at some point.
>>
>>> This is equivalent to providing the offset definitions in the
>>> init functions, instead of at the top of the file.
>>
>> Sorry, my brain parses text far better than hex number.
> 
> Well, the hex numbers do need to show up somewhere :-)
> 
> IIUC, you're saying that
> #define MUX_OFFSET 0x48
> is clearer than
> pcie->mux = base + 0x48;

yes.

> 
> OK, I can accept that. Maybe our brains have been trained
> to easily recognize and ingest the macro, or maybe it's
> the caps, or maybe the fact that the statement does
> several things (addition and assignment and hex).
> 
> Out of curiosity, how would you feel about
> pcie->MUX_OFFSET = 0x48;
> and then using
> readl_relaxed(pcie->base + pcie->MUX_OFFSET);
> 
> It feels weird to me, I think mostly because it is
> an unusual pattern.

Exactly. Use existing practices help the reviewers quite a lot.

> 
> Anyway, I'll add the macros, if that improves review and
> maintenance.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...