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Date:   Fri, 15 Mar 2019 09:34:29 +0100
From:   Miquel Raynal <miquel.raynal@bootlin.com>
To:     Masahiro Yamada <yamada.masahiro@socionext.com>
Cc:     Boris Brezillon <bbrezillon@kernel.org>,
        Richard Weinberger <richard@nod.at>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Marek Vasut <marek.vasut@gmail.com>,
        linux-mtd <linux-mtd@lists.infradead.org>,
        Brian Norris <computersforpeace@gmail.com>,
        David Woodhouse <dwmw2@infradead.org>
Subject: Re: [PATCH v3 2/9] mtd: rawnand: denali: refactor syndrome layout
 handling for raw access
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Hi Masahiro,

Masahiro Yamada <yamada.masahiro@socionext.com> wrote on Thu, 14 Mar
2019 17:24:41 +0900:

> Hi Miquel,
> 
> On Tue, Mar 12, 2019 at 10:13 PM Miquel Raynal
> <miquel.raynal@bootlin.com> wrote:
> >
> > Hi Masahiro,
> >
> > Masahiro Yamada <yamada.masahiro@socionext.com> wrote on Tue, 12 Mar
> > 2019 20:07:27 +0900:
> >  
> > > Hi Miquel,
> > >
> > >
> > > On Tue, Mar 12, 2019 at 7:54 PM Miquel Raynal <miquel.raynal@bootlin.com> wrote:  
> > > >
> > > > Hi Masahiro,
> > > >
> > > > Masahiro Yamada <yamada.masahiro@socionext.com> wrote on Tue, 12 Mar
> > > > 2019 19:51:21 +0900:
> > > >  
> > > > > On Tue, Mar 12, 2019 at 7:28 PM Miquel Raynal <miquel.raynal@bootlin.com> wrote:  
> > > > > >
> > > > > > Hi Masahiro,
> > > > > >
> > > > > > Masahiro Yamada <yamada.masahiro@socionext.com> wrote on Tue, 12 Mar
> > > > > > 2019 17:44:43 +0900:
> > > > > >  
> > > > > > > The Denali IP adopts the syndrome page layout (payload and ECC are
> > > > > > > interleaved). The *_page_raw() and *_oob() callbacks are complicated
> > > > > > > because they must hide the underlying layout used by the hardware,
> > > > > > > and always return contiguous in-band and out-of-band data.
> > > > > > >
> > > > > > > Currently, similar code is duplicated to reorganize the data layout.
> > > > > > > For example, denali_read_page_raw() and denali_write_page_raw() look
> > > > > > > almost the same.
> > > > > > >
> > > > > > > The idea for refactoring is to split the code into two parts:
> > > > > > >   [1] conversion of page layout
> > > > > > >   [2] what to do at every ECC chunk boundary
> > > > > > >
> > > > > > > For [1], I wrote denali_raw_payload_op() and denali_raw_oob_op().
> > > > > > > They manipulate data for the Denali controller's specific page layout
> > > > > > > of in-band, out-of-band, respectively.
> > > > > > >
> > > > > > > The difference between write and read is just the operation at
> > > > > > > ECC chunk boundaries. For example, denali_read_oob() calls
> > > > > > > nand_change_read_column_op(), whereas denali_write_oob() calls
> > > > > > > nand_change_write_column_op(). So, I implemented [2] as a callback
> > > > > > > passed into [1].
> > > > > > >
> > > > > > > Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> > > > > > > ---
> > > > > > >  
> > > > > >
> > > > > > [...]
> > > > > >  
> > > > > > >  static int denali_read_page_raw(struct nand_chip *chip, uint8_t *buf,
> > > > > > >                               int oob_required, int page)
> > > > > > >  {
> > > > > > > +     struct denali_nand_info *denali = to_denali(chip);
> > > > > > >       struct mtd_info *mtd = nand_to_mtd(chip);
> > > > > > > -     struct denali_nand_info *denali = mtd_to_denali(mtd);
> > > > > > > -     int writesize = mtd->writesize;
> > > > > > > -     int oobsize = mtd->oobsize;
> > > > > > > -     int ecc_steps = chip->ecc.steps;
> > > > > > > -     int ecc_size = chip->ecc.size;
> > > > > > > -     int ecc_bytes = chip->ecc.bytes;
> > > > > > >       void *tmp_buf = denali->buf;
> > > > > > > -     int oob_skip = denali->oob_skip_bytes;
> > > > > > > -     size_t size = writesize + oobsize;
> > > > > > > -     int ret, i, pos, len;
> > > > > > > +     size_t size = mtd->writesize + mtd->oobsize;
> > > > > > > +     int ret;
> > > > > > > +
> > > > > > > +     if (!buf)
> > > > > > > +             return -EINVAL;
> > > > > > >
> > > > > > >       ret = denali_data_xfer(chip, tmp_buf, size, page, 1, 0);
> > > > > > >       if (ret)
> > > > > > >               return ret;
> > > > > > >
> > > > > > > -     /* Arrange the buffer for syndrome payload/ecc layout */
> > > > > > > -     if (buf) {
> > > > > > > -             for (i = 0; i < ecc_steps; i++) {
> > > > > > > -                     pos = i * (ecc_size + ecc_bytes);
> > > > > > > -                     len = ecc_size;
> > > > > > > -
> > > > > > > -                     if (pos >= writesize)
> > > > > > > -                             pos += oob_skip;
> > > > > > > -                     else if (pos + len > writesize)
> > > > > > > -                             len = writesize - pos;
> > > > > > > -
> > > > > > > -                     memcpy(buf, tmp_buf + pos, len);
> > > > > > > -                     buf += len;
> > > > > > > -                     if (len < ecc_size) {
> > > > > > > -                             len = ecc_size - len;
> > > > > > > -                             memcpy(buf, tmp_buf + writesize + oob_skip,
> > > > > > > -                                    len);
> > > > > > > -                             buf += len;
> > > > > > > -                     }
> > > > > > > -             }
> > > > > > > -     }
> > > > > > > +     ret = denali_raw_payload_op(chip, buf, denali_memcpy_in, tmp_buf);  
> > > > > >
> > > > > > Honestly, I still don't like passing denali_memcpy_in/out as parameter.
> > > > > >
> > > > > > Besides that, once you'll have added helpers to avoid abusing the
> > > > > > ternary operator in 4/9, the rest looks fine by me.
> > > > > >  
> > > > >
> > > > >
> > > > > Do you have any suggestion?  
> > > >
> > > > Maybe register these two helpers at probe as controller specific hooks,
> > > > then just pass an in/out boolean to the function?
> > > >  
> > >
> > > Sorry, I do not understand.
> > >
> > > Are you suggesting to do like follows in probe ?
> > >
> > > denali->change_column_read_raw = denali_memcpy_in;
> > > denali->change_column_write_raw = denali_memcpy_out;
> > > denali->change_column_read_oob = denali_change_read_column_op;
> > > denali->change_column_write_oob = denali_change_write_column_op;
> > >
> > >
> > > All the 4 hooks are always needed
> > > regardless of any probed features.
> > >
> > >
> > > The result is just textual replacement
> > > denali_* with denali->*.
> > >
> > > What's the point of copying fixed function addresses
> > > to denali structure?
> > >
> > >  
> >
> > What I don't like is the function pointer as a function parameter.  
> 
> This is a usual way to handle callback.
> 
> > You
> > can use the functions defined statically if you prefer as long as the
> > parameter is just a boolean for instance?  
> 
> 
> 
> I still do not understand your concern,
> but if you ban the use of function pointer,
> the following is the best I can do
> since there are 4 hooks depending on the
> combination of oob/raw, write/read.
> 
> 
> 
> if (oob) {
>         if (write)
>                 return nand_change_write_column_op(chip, offset, buf,
>                                                    len, false);
>         else
>                 return nand_change_read_column_op(chip, offset, buf,
>                                                   len, false);
> }
> 
> if (write)
>         memcpy(denali->buf + offset, buf, len);
> else
>         memcpy(buf, denali->buf + offset, len);
> 
> return 0;

No, I meant passing a boolean to denali_raw_payload_op() instead of a
function pointer. Then from denali_raw_payload_op(), intead of doing

ret = cb();
if (ret)
        ...

doing:

if (read)
        ret = denali_memcpy_in()
else
        ret = denali_memcpy_out()

if (ret)
        ...

But nevermind, if this is bothering you too much let's keep the current
form, it's fine.

> 
> 
> BTW, when are .read_page_raw / .write_page_raw used?

I'm not sure what is the question here but these hooks are important
and allow to test the driver. nandbiterrs use them (although we do
not care about the performance in these hooks).

> 
> Currently, I use "whole page access && memcpy" for better performance.
> 
> If those hooks are rarely used, I use
> nand_change_write_column_op / nand_change_read_column_op,
> which will reduce the if-conditional.

Yes you can. We do not care about performance in raw accessors.

Thanks,
Miquèl