linux-kernel - Re: [PATCH 3/7] mtd: spi-nor: add restriction for nmaps in smpt parser

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Date:   Thu, 8 Nov 2018 14:08:26 +0100
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     <Tudor.Ambarus@...rochip.com>
Cc:     <marek.vasut@...il.com>, <dwmw2@...radead.org>,
        <computersforpeace@...il.com>, <richard@....at>,
        <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <yogeshnarayan.gaur@....com>, <cyrille.pitchen@...ev4u.fr>
Subject: Re: [PATCH 3/7] mtd: spi-nor: add restriction for nmaps in smpt
 parser

On Thu, 8 Nov 2018 13:54:47 +0100
Boris Brezillon <boris.brezillon@...tlin.com> wrote:

> > -	while (i < smpt_len) {
> > +	for (nmaps = 0; i < smpt_len; nmaps++) {
> > +		/*
> > +		 * The map selector is limited to a maximum of 8 bits, allowing
> > +		 * for a maximum of 256 possible map configurations. The total
> > +		 * number of map configurations should be addressable by the
> > +		 * total number of bits described by the detection commands.
> > +		 */
> > +		if (ncmds && nmaps >= (1 << (ncmds + 1)))
> > +			break;
> > +  
> 
> Maybe I missed something but it sounds like this change is just
> optimizing the SPMT parsing a bit, and to be honest, I'm not sure this
> is really needed. Most of the time, smpt_len will be rather small, so
> trying to bail out earlier is not bringing much perf improvements.

To make it clearer, I don't think the extra complexity is worth the tiny
perf improvement.