linux-kernel - Re: [PATCH v4 02/10] mtd: st_spi_fsm: Fetch boot device locations from DT match tables

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Message-ID: <20150224050452.GG18140@ld-irv-0074>
Date:	Mon, 23 Feb 2015 21:04:52 -0800
From:	Brian Norris <computersforpeace@...il.com>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kernel@...inux.com, linux-mtd@...ts.infradead.org,
	devicetree@...r.kernel.org
Subject: Re: [PATCH v4 02/10] mtd: st_spi_fsm: Fetch boot device locations
 from DT match tables

On Tue, Feb 10, 2015 at 03:46:34PM +0800, Lee Jones wrote:
> On Thu, 05 Feb 2015, Brian Norris wrote:
> > On Wed, Jan 21, 2015 at 03:24:20PM +0000, Lee Jones wrote:
> > > To trim down on the amount of properties used by this driver and to conform
> > > to the newly agreed method of acquiring syscfg registers/offsets, we now
> > > obtain this information using match tables.
> > 
> > Where did this agreement happen? Are you only referring to the previous
> > patch?
> 
> I think your interpretation of the above text and my intentions are
> not the same.

To be clear: I'm simply asking what do you mean by "agreed method". I
never agreed to syscfg registers/offsets. So who did? Are you agreeing
with yourself?

> I have no idea why there is a different configuration
> depending on if we booted from SPI NOR or not and hence can not answer
> your query below.

Seriously? That's all you can come up with? Sheesh. And you wonder why I
called you out on not understanding the code that you're sending me.

> The description above is pertaining to the
> different/new way in which we obtain and request syscfg registers.

OK. So you're dealing with the "how" but not the "why." That is not a
reasonable way to develop good code.

> In previous incarnations of this patchset, we were defining new vendor
> specific properties in order to request and register and the mask:
> 
>   st,boot-device-reg = <0x958>;
>   st,boot-device-spi = <0x1a>;
> 
> ... this is not optimal, as DT properties should only be created if
> there are no other way to obtain platform specific information.  As
> there are few supported platforms and this configuration does not
> change through variants, we are now supplying it via static tables,
> which can be obtained easily using the DT match framework.

I understand what you're doing with syscfg and these register offsets.
But if you follow the code as to what they're actually producing, you
see that it yields the 'booted_from_spi' boolean. That's a pretty simple
concept.

Now, unless you were able to provide an additional enlightening
viewpoint, then the following paragraph likely all holds true:

> > Also, I realized that all this boot device / syscfg gymnastics is just
> > for one simple fact; your driver is trying to hide the fact that your
> > system can't reliably handle 4-byte addressing for the boot device. Even
> > if you try your best at toggling 4-byte addressing before/after each
> > read/write/erase, you still are vulnerable to power cuts during the
> > operation. This is a bad design, and we have consistently agreed that we
> > aren't going to work around that in Linux.
> > 
> > Better solutions: hook up a reset line to your flash; improve your boot
> > ROM / bootloader to handle 4-byte addressing for large flash.
> 
> You have reached the boundaries of my knowledge on this.  Perhaps
> Angus (BCC'ed) would be kind enough to assist.

And so we have also reached the boundaries of my willingness to review
your code. There's a significant technical point here that drove you to
define several new DT compatible strings. I propose (and am now more
convinced) that this is not actually necessary. But apparently you are
not equipped to have a discussion about this.

I'm tempted to:

  git rm drivers/mtd/devices/st_spi_fsm.c

(Along with the appropriate Kconfig and Makefile entries, of course.)

> > What's the possibility of dropping all this 4-byte address toggling
> > shenanigans? This will be a blocker to merging with spi-nor.c.

Brian
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