linux-kernel - Re: [PATCH 1/4] Blackfin: arch patch for 2.6.18

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Message-ID: <ef35o5$vo4$1@sea.gmane.org>
Date:	Sat, 23 Sep 2006 11:28:05 +0000 (UTC)
From:	"Matthieu CASTET" <castet.matthieu@...e.fr>
To:	linux-kernel@...r.kernel.org
Subject:  Re: [PATCH 1/4] Blackfin: arch patch for 2.6.18

Hi,

On Sat, 23 Sep 2006 02:50:02 -0400, Mike Frysinger wrote:

>> It would be nice if you could use a generic way to pass this partition data
>> to the kernel from the mtd medium, instead of hardcoding it here.
> 
> i often wish for such things myself :)
> 
> unfortunately, the boot loader we utilize (u-boot) isnt exactly
> friendly to the idea of managing flash partitions like redboot, and
> what we have here is the current standard method for defining flash
> partitions with mtd
> 

humm you could use cmdlinepart [1] and pass the partition as a kernel
string with uboot.

That's what we are doing and it works perfectly.

>> > +/* Clock and System Control (0xFFC0 0400-0xFFC0 07FF) */
>> > +#define bfin_read_PLL_CTL()                  bfin_read16(PLL_CTL)
>> > +#define bfin_write_PLL_CTL(val)              bfin_write16(PLL_CTL,val)
>> > +#define bfin_read_PLL_STAT()                 bfin_read16(PLL_STAT)
>> (and 700 more of these)
>>
>> What's the point, are you getting paid by lines of code? Just use
>> the registers directly!
> 
> in our last submission we were doing exactly that ... and we were told
> to switch to a function style method of reading/writing memory mapped
> registers
hum, IRRC in your last submission you used volatile to read/write register.
Some people told you that volatile are evil and you should use a function
to read them.

But there no need to these defines. Just use bfin_read16(register_name) in
your code.

For an example look at arch/mips/au1000/common/usbdev.c for a driver using
memory mapped register.
Also you could use standard function like readl/writel if there no special
constraint (on the example a special function is needed because
readl/writel do some byteswapping on that platform (need for external
device), that is not need for memory mapped register).

Hope it will help you to improve your code.

Matthieu

[1]
see drivers/mtd/cmdlinepart.c for more information.
For example 
1 NOR Flash with 2 partitions, 1 NAND with one
 edb7312-nor:256k(ARMboot)ro,-(root);edb7312-nand:-(home)

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