Re: [PATCH v4 2/4] mtd: nand: gpmi: add gpmi_move_bits function

[Boris Brezillon <boris.brezillon@free-electrons.com>]

On Thu, 20 Nov 2014 01:22:09 -0800
Brian Norris <computersforpeace@gmail.com> wrote:

> On Mon, Oct 20, 2014 at 10:46:15AM +0200, Boris Brezillon wrote:
> > Add a new function to move bits (not bytes) from a memory region to
> > another one.
> > This function is similar to memmove except it acts at bit level.
> > This function is needed to implement GPMI raw access functions, given the
> > fact that ECC engine does not pad ECC bits to the next byte boundary.
> > 
> > Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
> > ---
> >  drivers/mtd/nand/gpmi-nand/gpmi-lib.c  | 129 +++++++++++++++++++++++++++++++++
> >  drivers/mtd/nand/gpmi-nand/gpmi-nand.h |   4 +
> >  2 files changed, 133 insertions(+)
> > 
> > diff --git a/drivers/mtd/nand/gpmi-nand/gpmi-lib.c b/drivers/mtd/nand/gpmi-nand/gpmi-lib.c
> > index 87e658c..5d4f140 100644
> > --- a/drivers/mtd/nand/gpmi-nand/gpmi-lib.c
> > +++ b/drivers/mtd/nand/gpmi-nand/gpmi-lib.c
> > @@ -1353,3 +1353,132 @@ int gpmi_read_page(struct gpmi_nand_data *this,
> >  	set_dma_type(this, DMA_FOR_READ_ECC_PAGE);
> >  	return start_dma_with_bch_irq(this, desc);
> >  }
> > +
> > +void gpmi_move_bits(u8 *dst, size_t dst_bit_off,
> > +		    const u8 *src, size_t src_bit_off,
> > +		    size_t nbits)
> 
> Two things:
> 
>  1) Yikes! This function is a little hairy.

Yes I know, and if you see a much simpler algorithm to do that, I'm
really interested :-).

> 
>  2) This function really deserves a full comment header (kerneldoc?); it
>  needs to have clearly-documented high-level semantics.

I'll add a kernel doc header.

> 
> I'm not sure how to address #1, as the complexity is necessary. Did you
> run this through some unit tests, at least?

No, but I did test it with several ECC configs.
Anyway, if I develop such unit tests, do you want me to put them in the
driver code (under an #ifdef section) ?


-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com