linux-kernel - Re: [PATCH] ARM: pxa: support 806MHz operating points for PXA31x processors A2 stepping

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Date:	Tue, 22 Feb 2011 18:38:40 +0800
From:	Axel Lin <axel.lin@...il.com>
To:	Igor Grinberg <grinberg@...pulab.co.il>
Cc:	linux-kernel@...r.kernel.org, Eric Miao <eric.y.miao@...il.com>,
	Russell King <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] ARM: pxa: support 806MHz operating points for PXA31x
 processors A2 stepping

2011/2/22 Igor Grinberg <grinberg@...pulab.co.il>:
> Hi,
>
> On 02/22/11 03:12, Axel Lin wrote:
>
>> Hi Igor,
>>
>>> Also, there is one thing that is not related to this patch, but
>>> if you have the hardware, you need to be concerned with,
>>> is that the vcc_core voltage has to be 1.4V, otherwise your
>>> hardware will be unstable.
>> I don't see any unstable issue on my device.
>> But it seems the vcc_core and vcc_sram fields of pxa3xx_freq_info
>> are not used now.
>
> Indeed, they are not used, because we don't have any DVFS driver for PXA3xx.
> But, the hardware is running regardless of you have the driver or not ;)
> There are other means to make sure the vcc_core voltage is set appropriately:
> 1) could be already set (PMIC default)
> 2) could be set by "Hardware-Controlled Voltage-Change Sequencer" automatically
>   (PXA3xx_DM_Vol_I chapter 6.8.3) if your PMIC is 100% compatible with PXA3xx
>   and PVCR[FVE/PVE] bits set accordingly.
> 3) If your PMIC is for some reason not 100% compatible, then the voltage can be
>   set by regulator API or even by the bootloader.
>
> Anyway, to make sure it is set to the appropriate level, you need to measure it.
> Usually, this line has some capacitors on it, so it shouldn't be a hard task
>
Thanks for the information. I'll check my settings.

> Now, regarding hardware instability:
> I've seen instabilities related to the vcc_core set improperly, but it has never
> showed up that quickly, sometimes it took a week of testing for it to show up.
> But when it shows up, you can see strange things happening, like your DRAM
> is messed or buses fail or the cpu just freezes.
>
>
> Another thing (which could be related to the patch) is the package marking.
> We have PXA3xx SoCs marked A2 stepping, but C624, which means that the
> highest running frequency should not exceed 624MHz.

This means not all PXA310 A2 stepping supports 806Mhz.
Can we differentiate the Cxxx option in software?

> What is your PXA3xx A2 marking in respect to Cxxx option?

Mine is 88AP310-A2-BGK2C806.

Regards,
Axel
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