linux-kernel - Re: [PATCH v4 4/7] ARM: l2c: Add support for overriding prefetch settings

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Date:	Fri, 19 Sep 2014 11:50:01 +0200
From:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:	Tomasz Figa <t.figa@...sung.com>
Cc:	linux-samsung-soc@...r.kernel.org,
	Kukjin Kim <kgene.kim@...sung.com>, lauraa@...eaurora.org,
	tony@...mide.com, linus.walleij@...aro.org,
	linux-kernel@...r.kernel.org, drake@...lessm.com,
	loeliger@...il.com, santosh.shilimkar@...com,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	linux-omap@...r.kernel.org, Tomasz Figa <tomasz.figa@...il.com>,
	linux-arm-kernel@...ts.infradead.org,
	Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH v4 4/7] ARM: l2c: Add support for overriding prefetch
 settings

On 26/08/2014 at 16:17:57 +0200, Tomasz Figa wrote :
> Firmware on certain boards (e.g. ODROID-U3) can leave incorrect L2C prefetch
> settings configured in registers leading to crashes if L2C is enabled
> without overriding them. This patch introduces bindings to enable
> prefetch settings to be specified from DT and necessary support in the
> driver.
> 
> Signed-off-by: Tomasz Figa <t.figa@...sung.com>

Tested-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>

It is working and useful on Atmel's sama5d4 were the bootloader is not
configuring the L2C prefetch. However, I'm wondering whether we should
add support for setting L310_PREFETCH_CTRL_DATA_PREFETCH and
L310_PREFETCH_CTRL_INSTR_PREFETCH. I'm currently doing it by using
".l2c_aux_val    = L310_AUX_CTRL_DATA_PREFETCH |
L310_AUX_CTRL_INSTR_PREFETCH" (those are the same bits) but this has the
disadvantage of displaying the "L2C: platform modifies aux control
register:" twice.

> +	if (!of_property_read_u32(np, "arm,prefetch-offset", &val)) {
> +		prefetch &= ~L310_PREFETCH_CTRL_OFFSET_MASK;
> +		prefetch |= val & L310_PREFETCH_CTRL_OFFSET_MASK;
> +	}
> +

While you use val directly here, later, while printing the offset, val +
1 is used. Maybe it would be better to have the same number in both
places, else you end up with having "arm,prefetch-offset = <1>" in your
DT and the kernel printing "L2C-310 ID prefetch enabled, offset 2
lines".

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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