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

From: Alexandre Belloni
Date: Fri Sep 19 2014 - 05:50:12 EST

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@xxxxxxxxxxx>

Tested-by: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxxxxxxxxx>

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

Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
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