linux-kernel - Re: [RFC PATCH 3/8] mtd: rawnand: ams-delta: Set port direction once per transfer

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Date:   Fri, 20 Jul 2018 21:29:10 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Janusz Krzysztofik <jmkrzyszt@...il.com>
Cc:     Miquel Raynal <miquel.raynal@...tlin.com>,
        Tony Lindgren <tony@...mide.com>,
        Aaro Koskinen <aaro.koskinen@....fi>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Santosh Shilimkar <ssantosh@...nel.org>,
        Kevin Hilman <khilman@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Richard Weinberger <richard@....at>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Marek Vasut <marek.vasut@...il.com>,
        linux-mtd@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-omap@...r.kernel.org,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>
Subject: Re: [RFC PATCH 3/8] mtd: rawnand: ams-delta: Set port direction
 once per transfer

On Fri, 20 Jul 2018 20:12:05 +0200
Janusz Krzysztofik <jmkrzyszt@...il.com> wrote:

> On Thursday, July 19, 2018 8:23:18 AM CEST Boris Brezillon wrote:
> > On Thu, 19 Jul 2018 01:57:05 +0200
> > Janusz Krzysztofik <jmkrzyszt@...il.com> wrote:
> >   
> > > In its current shape, the driver sets data port direction before each
> > > byte read/write operation, even during multi-byte transfers.  Optimize
> > > that by setting the port direction only on first byte of each transfer.  
> > 
> > Sounds like premature optimization for something you'll rework when
> > fully switching to the GPIO consumer API to control the DATA bus.  
> 
> Indeed, this optimization was crucial for getting acceptable performance of 
> data transfers over GPIO.  I'm only not sure if there is any action in 
> response to your comment expected on my side, e.g., did you want to say I 
> should modify the patch description, or change the order of patches?

I'm just saying that, since you switch to a solution that goes through
the GPIO framework to control the data bus, making sure the the pin
direction change is done only once when reading/writing several bytes is
something you can do after/when transitioning to the new approach.

So yes, I suggest to re-order patches, except that this patch won't
look the same at all if you move it after the "use the GPIO consumer
API to control data bus" patch.