linux-kernel - Re: [PATCH RESEND] ARM: dts: keystone-k2*: Increase SPI Flash partition size for U-Boot

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Message-ID: <20161012115703.GE1041@n2100.armlinux.org.uk>
Date:   Wed, 12 Oct 2016 12:57:03 +0100
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Vignesh R <vigneshr@...com>
Cc:     Santosh Shilimkar <ssantosh@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Muralidharan Karicheri <m-karicheri2@...com>
Subject: Re: [PATCH RESEND] ARM: dts: keystone-k2*: Increase SPI Flash
 partition size for U-Boot

On Wed, Oct 12, 2016 at 04:30:28PM +0530, Vignesh R wrote:
> Hi,
> 
> On Monday 10 October 2016 08:01 PM, Russell King - ARM Linux wrote:
> > On Mon, Oct 10, 2016 at 07:41:41PM +0530, Vignesh R wrote:
> >> U-Boot SPI Boot image is now more than 512KB for Keystone2 devices and
> >> cannot fit into existing partition. So, increase the SPI Flash partition
> >> for U-Boot to 1MB for all Keystone2 devices.
> >>
> >> Signed-off-by: Vignesh R <vigneshr@...com>
> >> ---
> >>
> >> This was submitted to v4.9 merge window but was never picked up:
> >> https://patchwork.kernel.org/patch/9135023/
> > 
> > I think you need to explain why it's safe to change the layout of the
> > flash partitions like this.
> > 
> > - What is this "misc" partition?
> > 
> 
> This partition seems to exists from the very beginning.  I believe, this
> is just a spare area of flash that can be used as per end-user
> requirement. Either to store a small filesystem or kernel. Copying
> Murali who added above partition if he has any input here.
> 
> > - Why is it safe to move the "misc" partition in this way?
> > 
> > - Do users need to do anything with data stored in the "misc" partition
> >   when changing kernels?
> > 
> 
> MTD layer will take care of most abstractions (like start address etc).
> Will add a note in commit message informing about the reduction in size
> of the partition.
> 
> > If the "misc" partition is simply unused space on the flash device, why
> > list it in DT?
> > 
> 
> If the unused space is not listed in the DT, then there is no /dev/mtdX
> node created for the unused section. User will then have to manually
> edit DT, in order to get the node and mount it. Instead, lets make it
> available by default.

So, taken all together, your argument is:

- We want a user partition
- It's okay to destroy the data in the user's partition by moving it
  around randomly between kernel versions.

The two do not naturally go together at all.  You're messing with user
expectations in ways you should not be.  This really is not an acceptable
approach.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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