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Re: [PATCH] MIPS: Fix errata for some 1074K cores.

To: Florian Fainelli <f.fainelli@gmail.com>
Subject: Re: [PATCH] MIPS: Fix errata for some 1074K cores.
From: Paul Burton <paul.burton@imgtec.com>
Date: Thu, 12 Sep 2013 16:12:37 +0100
Cc: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>, "Steven J. Hill" <Steven.Hill@imgtec.com>, "linux-mips@linux-mips.org" <linux-mips@linux-mips.org>, "ralf@linux-mips.org" <ralf@linux-mips.org>
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Agreed, my point is not about your code but your commit message. If I'm reading a commit which works around CPU errata I should not have to go and ask the hardware engineers or even read an errata document in order to know what you're doing. Your commit message should explain the errata, its effects and how your patch works around the problem.

Paul

On 12/09/13 16:05, Florian Fainelli wrote:
2013/9/12 Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>:
Treat it as is.

It is a dirty laundry of HW engineers and you may need to communicate with them 
or read Errata docs on CPU.

If it is about a way how it is written - ask Steven, initially it was in 
mainland probe code but he think it should be a separate function. I just 
corrected him, pointing that erratas on 74K and 1074K are different. But 
because he insist on having the same CPU_74K for both, so...
If you take a look at another CPU company such as ARM, they provide
lengthy explanations for their various Erratas:

config PJ4B_ERRATA_4742
         bool "PJ4B Errata 4742: IDLE Wake Up Commands can Cause the
CPU Core to Cease Operation"
         depends on CPU_PJ4B && MACH_ARMADA_370
         default y
         help
           When coming out of either a Wait for Interrupt (WFI) or a Wait for
           Event (WFE) IDLE states, a specific timing sensitivity exists between
           the retiring WFI/WFE instructions and the newly issued subsequent
           instructions.  This sensitivity can result in a CPU hang scenario.
           Workaround:
           The software must insert either a Data Synchronization Barrier (DSB)
           or Data Memory Barrier (DMB) command immediately after the WFI/WFE
           instruction

I really think that you should aim for the same level of information
so that people know whether this is relevant for their platform,
whether they have the ECO applied etc...



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