linux-kernel - Re: [PATCH] mtd: rawnand: call onfi_fill_data_interface() once again after nand

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Date:   Fri, 8 Feb 2019 22:45:40 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        Boris Brezillon <bbrezillon@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mtd <linux-mtd@...ts.infradead.org>,
        Brian Norris <computersforpeace@...il.com>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH] mtd: rawnand: call onfi_fill_data_interface() once
 again after nand_detect

Hi Masahiro,

Masahiro Yamada <yamada.masahiro@...ionext.com> wrote on Fri, 8 Feb
2019 17:35:32 +0900:

> HI Miquel,
> 
> On Thu, Feb 7, 2019 at 10:02 PM Miquel Raynal <miquel.raynal@...tlin.com> wrote:
> >
> > Hi Masahiro,
> >
> > Masahiro Yamada <yamada.masahiro@...ionext.com> wrote on Thu, 7 Feb
> > 2019 19:46:54 +0900:
> >  
> > > On Thu, Feb 7, 2019 at 7:16 PM Miquel Raynal <miquel.raynal@...tlin.com> wrote:  
> > > >
> > > > Hi Masahiro,
> > > >
> > > > Masahiro Yamada <yamada.masahiro@...ionext.com> wrote on Thu,  7 Feb
> > > > 2019 18:57:56 +0900:
> > > >  
> > > > > nand_scan_ident() calls onfi_fill_data_interface() at its entry
> > > > > to set up the initial timing parameters.
> > > > >
> > > > > The timing parameters are needed not only for ->setup_data_interface(),
> > > > > but also for giving the correct delay to NAND_OP_WAIT_RDY, for example.
> > > > >
> > > > > If the driver sets the NAND_KEEP_TIMINGS flag, or does not support  
> > > > > ->setup_data_interface() hook, those parameters will never updated.  
> > > >
> > > >                                                             ^ be  
> > >
> > > Will fix (if v2 is welcome)
> > >
> > >  
> > > > >
> > > > > Before nand_detect(), we never know whether the chip is ONFi or not.
> > > > > So, onfi_fill_data_interface() has to assume the worst case, i.e.
> > > > > non-ONFi.  
> > > >
> > > > s/ONFi/ONFI/?  
> > >
> > > Will fix.
> > >
> > > Looks like I was misunderstanding
> > > maybe because the letter 'I' in the logo
> > > (http://www.onfi.org/)
> > > looks like a lowercase...
> > >
> > >  
> >
> > Oh right. I don't know what's best. Pick your favorite :)
> >  
> > >
> > >  
> > > >  
> > > > >
> > > > > After nand_detect(), if the chip turns out to be ONFi-compliant,
> > > > > we can optimize tPROG_max, tBERS_max, etc.
> > > > >
> > > > > Call onfi_fill_data_interface() once again.  
> > > >
> > > > Sorry but I don't get why this is needed as there is the same call at
> > > > the top of this function. Can you be more specific on where/when the
> > > > missing call produces a failure?  
> > >
> > >
> > > onfi_fill_data_interface() sets different values
> > > for tPROG_max, tBER_max, tR_max, tCCS_min
> > > depending on whether the chip is ONFI or not.
> > >
> > > For the first call, onfi_fill_data_interface()
> > > chooses the else-part since we never know
> > > the chip specification at this point.
> > >
> > > If we call onfi_fill_data_interface() once again
> > > after nand_detect(), it may choose the if-part.
> > >
> > >
> > > If a driver supports ->setup_data_interface(),
> > > nand_init_data_interface() will set the optimal
> > > timing parameters anyway.
> > >
> > > But, if a driver does not support ->setup_data_interface(),
> > > it will not happen since nand_has_setup_data_iface() returns false.  
> >
> > And I think this is the expected behavior. Calling again
> > onfi_fill_data_interface() would probably enhance a bit the timings.
> > The effect is that later exchanges with the NAND chip would be just a
> > bit faster. But if you care about performance, then why not implementing  
> > ->setup_data_interface()? Even a dummy implementation would do the  
> > trick: only accept timing mode 0 without any changes on the controller
> > side.  
> 
> 
> My driver (denali) does implement ->setup_data_interface().

Fortunately, yes! :)

> 
> When I was testing this thoroughly on my board,
> I noticed the timing parameters were slightly changed
> after nand_detect() detected ONFI chip.

I see.

> 
> > Unless you give me a use case where this is not possible, I don't think
> > it is worth changing this path.  
> 
> Only the use case I can come up with is when NAND_KEEP_TIMINGS was set.
> But, it is just a matter of timeout values.
> 
> So, please throw away this patch.

Ok!


Thanks anyway for the proposal!
Miquèl