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

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Date:   Thu, 7 Feb 2019 14:01:36 +0100
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     linux-mtd <linux-mtd@...ts.infradead.org>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Brian Norris <computersforpeace@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        David Woodhouse <dwmw2@...radead.org>,
        Boris Brezillon <bbrezillon@...nel.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 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.

Unless you give me a use case where this is not possible, I don't think
it is worth changing this path.


Thanks,
Miquèl