From: marc_gonzalez@sigmadesigns•com (Marc Gonzalez)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v3] arm-soc: Add support for Sigma Designs Tango4
Date: Tue, 20 Oct 2015 11:50:14 +0200 [thread overview]
Message-ID: <56260E56.10403@sigmadesigns.com> (raw)
In-Reply-To: <CAL_Jsq+jthx9ffnUm-G-TV9LdxBRp3SKyhyfcVu=7kN3CuumJw@mail.gmail.com>
On 19/10/2015 18:39, Rob Herring wrote:
> Marc Gonzalez wrote:
>
>> About the cache controller, I was confused by this comment:
>> /*
>> * Always enable non-secure access to the lockdown registers -
>> * we write to them as part of the L2C enable sequence so they
>> * need to be accessible.
>> */
>> l2x0_saved_regs.aux_ctrl = aux | L310_AUX_CTRL_NS_LOCKDOWN;
>>
>> I see no lock() function, only unlock().
>>
>> But the unlock function merely writes 0 to the relevant registers,
>> and 0 is the value at reset for those registers. Since nothing ever
>> sets the registers to non-zero, why is the unlock needed at all?
>
> It was because some bootloaders set those registers. Linux just wants
> them to be all unlocked.
I see.
My problem then, is that my current firmware does not set L310_AUX_CTRL_NS_LOCKDOWN
and does not allow updating that bit.
So when l2c_unlock() is called, Linux (running in non-secure mode)
tries to write to read-only registers:
> On reset, the Non-Secure Lockdown Enable bit is set to 0 and Lockdown
> Registers are not permitted to be modified by non-secure accesses. In
> that configuration, if a non-secure access tries to write to those
> registers, the write response returns a DECERR response. This decode
> error results in the registers not being updated.
I suppose "a DECERR response" means Linux will oops?
I see several options to work-around this problem:
A) Have the firmware set L310_AUX_CTRL_NS_LOCKDOWN at boot
B) Have the firmware allow Linux to set L310_AUX_CTRL_NS_LOCKDOWN
C) Have a way in Linux to define .unlock as a NOP (trusting the
firmware to NOT have locked anything)
Perhaps adding a "no-unlock-required;" boolean property to the l2cc
node, which would override the .unlock method?
I'd like to hear suggestions on the "best" approach.
Regards.
next prev parent reply other threads:[~2015-10-20 9:50 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-02 16:02 [PATCH] arm-soc: Add Sigma Designs Tango4 port Mason
2015-10-02 16:10 ` Måns Rullgård
2015-10-02 16:33 ` Mason
2015-10-02 16:55 ` Måns Rullgård
2015-10-02 18:00 ` Mason
2015-10-02 17:13 ` Russell King - ARM Linux
2015-10-02 18:09 ` Mason
2015-10-02 18:53 ` Russell King - ARM Linux
2015-10-02 19:25 ` Mason
2015-10-02 19:56 ` Arnd Bergmann
2015-10-02 20:53 ` Mason
2015-10-02 21:11 ` Arnd Bergmann
2015-10-02 21:57 ` Mason
2015-10-02 22:12 ` Arnd Bergmann
2015-10-05 16:25 ` [PATCH v2] arm-soc: Add support for Sigma Designs Tango4 Marc Gonzalez
2015-10-06 15:57 ` [PATCH v3] " Marc Gonzalez
2015-10-09 13:18 ` Arnd Bergmann
2015-10-09 13:30 ` Marc Gonzalez
2015-10-09 14:40 ` Måns Rullgård
2015-10-09 19:01 ` Mason
2015-10-09 20:24 ` Måns Rullgård
2015-10-09 21:12 ` Mason
2015-10-09 14:08 ` Rob Herring
2015-10-09 14:16 ` Marc Gonzalez
2015-10-09 14:48 ` Rob Herring
2015-10-13 15:54 ` Marc Gonzalez
2015-10-13 17:55 ` Rob Herring
2015-10-19 11:09 ` Marc Gonzalez
2015-10-19 16:39 ` Rob Herring
2015-10-19 17:32 ` Mark Rutland
2015-10-20 9:20 ` Marc Gonzalez
2015-10-20 9:50 ` Marc Gonzalez [this message]
2015-10-20 10:04 ` Russell King - ARM Linux
2015-10-20 10:54 ` Marc Gonzalez
2015-10-09 14:12 ` [PATCH v2] " Rob Herring
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