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Date: Fri, 19 Sep 2014 20:30:07 +0200 From: Alexandre Belloni <alexandre.belloni@...e-electrons.com> To: Russell King - ARM Linux <linux@....linux.org.uk> Cc: Tomasz Figa <t.figa@...sung.com>, 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, 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 19/09/2014 at 17:39:32 +0100, Russell King - ARM Linux wrote : > On Fri, Sep 19, 2014 at 11:50:01AM +0200, Alexandre Belloni wrote: > > 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. > > The L2C documentation, freely available from the ARM infocentre website, > has the answer to this for you. > > The two bits in the prefetch control register which control the data > and instruction prefetching are aliases of the aux control register. > If you set them to a value in one register, they are reflected in the > other. > > The reason for that is that once the L2 cache is enabled, writes to > the aux control register are no longer permitted, but it's safe to > enable and disable the prefetching with the cache already enabled. > This reason is even stated in the documentation. > Yeah, so my question still holds, should we have an other way to enable/disable I/D prefetch by adding two other DT bindings ? -- Alexandre Belloni, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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