linux-kernel - Re: [PATCH v2 06/11] ARM:stixxxx: Add STiH415 SOC support

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Date:	Thu, 13 Jun 2013 14:47:27 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Srinivas KANDAGATLA <srinivas.kandagatla@...com>,
	Michal Simek <monstr@...str.eu>,
	linux-arm <linux-arm-kernel@...ts.infradead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnd Bergmann <arnd@...db.de>,
	"David S. Miller" <davem@...emloft.net>,
	devicetree-discuss <devicetree-discuss@...ts.ozlabs.org>,
	Grant Likely <grant.likely@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	John Stultz <john.stultz@...aro.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	Mark Brown <broonie@...nel.org>,
	Mauro Carvalho Chehab <mchehab@...hat.com>,
	Olof Johansson <olof@...om.net>,
	Rob Herring <rob.herring@...xeda.com>,
	Rob Landley <rob@...dley.net>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Stephen Gallimore <stephen.gallimore@...com>,
	Stuart Menefy <stuart.menefy@...com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tony Prisk <linux@...sktech.co.nz>
Subject: Re: [PATCH v2 06/11] ARM:stixxxx: Add STiH415 SOC support

On Tue, Jun 11, 2013 at 1:19 AM, Russell King - ARM Linux
<linux@....linux.org.uk> wrote:
> On Mon, Jun 10, 2013 at 12:46:59PM +0100, Srinivas KANDAGATLA wrote:
>> >     +       aux_ctrl = (0x1 << L2X0_AUX_CTRL_SHARE_OVERRIDE_SHIFT) |
>> >     +               (0x1 << L2X0_AUX_CTRL_DATA_PREFETCH_SHIFT) |
>> >     +               (0x1 << L2X0_AUX_CTRL_INSTR_PREFETCH_SHIFT) |
>> >     +               (way_size << L2X0_AUX_CTRL_WAY_SIZE_SHIFT);
>> >
>> >
>> >
>> > #include <linux/bitops.h>
>> > Linus Walleij would write use  BIT() here
>>
>> I will use BIT() macro.
>
> Without checking those fields... BIT() is only appropriate if you're
> really talking about single bits.  If you have a field of more than a
> single bit which you happen to be setting to '1' then it's not
> appropriate to use BIT().

This is true. Luckily I didn't push for it myself this time.

However, on a related key we have this hidden away in MFD
drivers/mfd/dbx500-prcmu-regs.h:

#define BITS(_start, _end) ((BIT(_end) - BIT(_start)) + BIT(_end))

It's used like so:

#define PRCM_PLL_FREQ_D_MASK    BITS(0, 7)

So you can define an multi-bit mask with a macro like that.

If there is interest in a construct like this I can make a patch to
move this thing to <linux/bitops.h>.

Yours,
Linus Walleij
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