linux-kernel - Re: [PATCH 05/30] amd64_edac: Cleanup chipselect handling

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Date:	Tue, 29 Mar 2011 12:39:09 -0300
From:	Mauro Carvalho Chehab <mchehab@...hat.com>
To:	Borislav Petkov <bp@...64.org>
CC:	"linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 05/30] amd64_edac: Cleanup chipselect handling

Em 29-03-2011 12:16, Borislav Petkov escreveu:
> On Tue, Mar 29, 2011 at 10:56:26AM -0400, Mauro Carvalho Chehab wrote:
>> Em 10-02-2011 15:15, Borislav Petkov escreveu:
>>> From: Borislav Petkov <borislav.petkov@....com>
>>>
>>> Add a struct representing the DRAM chip select base/limit register
>>> pairs. Concentrate all CS handling in a single function. Also, add CS
>>> looping macros for cleaner, more readable code. While at it, adjust code
>>> to F15h. Finally, do smaller macro names cleanups (remove family names
>>> from register macros) and debug messages clarification.
>>>
>>> No functional change.
>>>
>>> Signed-off-by: Borislav Petkov <borislav.petkov@....com>
>>
>> Hi Borislav,
>>
>>> --- a/drivers/edac/amd64_edac.h
>>> +++ b/drivers/edac/amd64_edac.h
>>> @@ -160,6 +160,14 @@
>>>  #define OFF false
>>>  
>>>  /*
>>> + * Create a contiguous bitmask starting at bit position @lo and ending at
>>> + * position @hi. For example
>>> + *
>>> + * GENMASK(21, 39) gives us the 64bit vector 0x000000ffffe00000.
>>> + */
>>> +#define GENMASK(lo, hi)			(((1ULL << ((hi) - (lo) + 1)) - 1) << (lo))
>>> +
>>
>> This is a nice macro that could be useful outside amd64. It is probably a good
>> idea to move it to include/linux/bitops.h.
> 
> I'd suggest rather <drivers/edac/edac_core.h> if you want to use it in
> EDAC. But if we have more users, I don't have a problem with putting
> it there (or somewhere else generic enough if people have a better
> suggestion).

Yeah, other edac drivers could benefit of using it, and also could benefit on a
variant that would do an AND operation and shift it, something like (untested):

/*
 * Create a contiguous bitmask starting at bit position @lo and ending at
 * position @hi. For example
 *
 * APPLY_BITMASK(v, 21, 39) will return the result of:
 * 	(v & 0x000000ffffe00000) >> 21
 */
#define APPLY_BITMASK(v, lo, hi)	(((v) & ((1ULL << ((hi) - (lo) + 1)) - 1) << (lo)) >> (lo))


Almost all edac drivers do something like the above, for example, to get DIMM rows/cols/banks, etc.

Probably, the most complex part is to find a nice name for it ;)

Yet, I think non-edac drivers could also benefit of such macro, and, as this is not
edac-specific, I think it would be better to add it at bitops.h.

Cheers,
Mauro

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