linux-kernel - Re: [PATCH 2/2] Add support for

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Date:	Wed, 27 Aug 2008 11:18:23 -0700
From:	Bruce_Leonard@...inc.com
To:	dedekind@...radead.org
Cc:	Bruce Leonard <brucle@...thlink.net>, linux-kernel@...r.kernel.org,
	linux-mtd@...ts.infradead.org,
	linux-mtd-bounces@...ts.infradead.org
Subject: Re: [PATCH 2/2] Add support for > 2GiB MTD devices

Artem,

> > +/*
> > + * Inline function for determining the size of the MTD device, 
independant
> > + * of old or new way of doing things.
> > + *
> > + */
> > +static inline u_int64_t device_size(struct mtd_info *a)
> > +{
> > +   return a->num_eraseblocks == 0 ? a->size : a->num_eraseblocks * 
a->erasesize;
> > +}
> 
> I do not think it is a good idea to do multiplication every time we need
> MTD device size. It is unnecessarily large overhead in terms of speed
> and code size.
> 

I'm still reluctant to change size to a 64-bit value.  There's a vague 
recolection of early conversations on the list that there would be little 
acceptance for that.  And that probably has to do with the ongoing 
conversation about ABI changes.  What I could do to eliminate the 
multiplication is introduce the same concept that the NAND layer uses, 
shift values.  After all, erasesize should always be a power of 2, making 
that a power of 2 multiplication which can be done via shifts.  By 
changing erasesize to erasesize_shift, I'd get something like this:

return a->num_eraseblocks == 0 ? a->size : a->num_eraseblocks << 
a->erasesize_shift

How would that suit you?

Bruce

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