linux-kernel - RE: [PATCH 2/2] arc: hsdk_defconfig: enable CONFIG_ARC_UBOOT

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Message-ID: <7h4l9ivvqj.fsf@baylibre.com>
Date:   Tue, 05 Feb 2019 12:14:12 -0800
From:   Kevin Hilman <khilman@...libre.com>
To:     Alexey Brodkin <alexey.brodkin@...opsys.com>,
        Vineet Gupta <vineet.gupta1@...opsys.com>,
        "clabbe\@baylibre.com" <clabbe@...libre.com>
Cc:     "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "alexey.brodkin\@synopsys.com" <alexey.brodkin@...opsys.com>,
        "linux-snps-arc\@lists.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        Eugeniy Paltsev <eugeniy.paltsev@...opsys.com>
Subject: RE: [PATCH 2/2] arc: hsdk_defconfig: enable CONFIG_ARC_UBOOT_SUPPORT

Alexey Brodkin <alexey.brodkin@...opsys.com> writes:

> Hi Vineet, Corentin,
>
>> -----Original Message-----
>> From: Vineet Gupta <vgupta@...opsys.com>
>> Sent: Tuesday, February 5, 2019 7:42 PM
>> To: Eugeniy Paltsev <paltsev@...opsys.com>; clabbe@...libre.com
>> Cc: linux-kernel@...r.kernel.org; alexey.brodkin@...opsys.com; khilman@...libre.com; linux-snps-
>> arc@...ts.infradead.org
>> Subject: Re: [PATCH 2/2] arc: hsdk_defconfig: enable CONFIG_ARC_UBOOT_SUPPORT
>> 
>> On 2/5/19 3:42 AM, Eugeniy Paltsev wrote:
>> > Hi Corentin,
>> >
>> > In case of devboards (like HSDK) we really often disable bootloader and load
>> > Linux image in memory via JTAG. Enabling CONFIG_ARC_UBOOT_SUPPORT by
>> > default will break it as we will try to interpret some junk in a registers
>> > as a pointers to bootargs/etc which aren't set by anyone in case of JTAG using.
>> >
>> > So it isn't a good idea to have CONFIG_ARC_UBOOT_SUPPORT enabled by default.
>> 
>> Right.
>> 
>> It is difficult to accommodate everyone's needs (often conflicting) in a single
>> defconfig.
>> Can you folks create an out-of-tree defconfig or some such.
>
> I do think there's a proper solution which [hopefully] makes both parties happy.
> Eugeniy is about to send-out a patch which allows us to not care about
> garbage in R0/R2 when running after U-Boot.

OK, cool, that sounds like a good workaround for the JTAG use case.

Just curious: what is the more common case for end-users?  u-boot or
JTAG?

At least on every other arch/board we use in kernelCI, u-boot is the
*much* more common load path than JTAG.  IMO, I would suggest that in
the case of unresolvable conflicts like, u-boot should be the normal
path, and JTAG would be the special case.

Anyways, hopefully the patch from Eugeniy works and gets rid of the
conflict. 

Related: if you end up accepting this series, they'll also need to be
backported to stable branches if we want to support them in kernelCI.

Kevin