linux-kernel - Re: [PATCH 1/2] GPIO: Add driver for Zynq GPIO controller

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Date:	Fri, 11 Apr 2014 08:57:25 +0200
From:	Michal Simek <monstr@...str.eu>
To:	Linus Walleij <linus.walleij@...aro.org>
CC:	Harini Katakam <harinikatakamlinux@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	Michal Simek <michal.simek@...inx.com>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Rob Landley <rob@...dley.net>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	michals@...inx.com, Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH 1/2] GPIO: Add driver for Zynq GPIO controller

On 04/10/2014 07:52 PM, Linus Walleij wrote:
> On Wed, Apr 2, 2014 at 7:56 AM, Michal Simek <monstr@...str.eu> wrote:
>> On 03/31/2014 10:22 AM, Linus Walleij wrote:
>>> On Sat, Mar 29, 2014 at 5:44 AM, Harini Katakam
>>> <harinikatakamlinux@...il.com> wrote:
>>>> On Sat, Mar 29, 2014 at 3:20 AM, Linus Walleij <linus.walleij@...aro.org> wrote:
>>>>> On Thu, Mar 27, 2014 at 4:25 PM, Harini Katakam <harinik@...inx.com> wrote:
>>>
>>>>>> +/* Read/Write access to the GPIO PS registers */
>>>>>> +static inline u32 zynq_gpio_readreg(void __iomem *offset)
>>>>>> +{
>>>>>> +       return readl_relaxed(offset);
>>>>>> +}
>>>>>> +
>>>>>> +static inline void zynq_gpio_writereg(void __iomem *offset, u32 val)
>>>>>> +{
>>>>>> +       writel_relaxed(val, offset);
>>>>>> +}
>>>>>
>>>>> I think this is unnecessary and confusing indirection.
>>>>> Just use the readl_relaxed/writel_relaxed functions directly in
>>>>> the code.
>>>>>
>>>>
>>>> This is just to be flexible.
>>>
>>> Define exactly what you mean with "flexible" in this context. I
>>> only see unnecessary overhead and hard-to-read code.
>>
>> We have just passed this discussion for watchdog driver
>> here: https://lkml.org/lkml/2014/4/1/843
>>
>> Are you ok with doing it in this way?
> 
> No :-)
> 
> Subsystem maintainers do not necessarily agree on such issues.

I think your sentence is right.  :-)
But what to do to convince you to agree with it?
We can use readl/writel directly (or relaxed versions) but it will
just end up that we will have a patch in our xilinx git tree
which won't be in the mainline.

Having central point for IO access functions it not an unused technique.
I was able to find out some cases in drivers/gpio/
gpio-bt8xx.c, gpio-msm-v1.c, gpio-tegra.c, gpio-xilinx.c (almost similar reason
here :-))
and just one in pinctrl-spear.h.
But I have to admit most of gpio/pinmux drivers are using them directly
but on the other hand they are not FPGA based. :-)

BTW: Shouldn't be __raw_ versions replaced by _relaxed?

Thanks,
Michal

-- 
Michal Simek, Ing. (M.Eng), OpenPGP -> KeyID: FE3D1F91
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel - Microblaze cpu - http://www.monstr.eu/fdt/
Maintainer of Linux kernel - Xilinx Zynq ARM architecture
Microblaze U-BOOT custodian and responsible for u-boot arm zynq platform



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