linux-kernel - Re: [PATCH] Revert "reset: microchip-sparx5: allow building as a module"

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Message-ID: <acddd598716d2d9e9903c425a3b54257@walle.cc>
Date:   Fri, 26 Aug 2022 13:37:37 +0200
From:   Michael Walle <michael@...le.cc>
To:     Philipp Zabel <p.zabel@...gutronix.de>
Cc:     Steen Hegelund <steen.hegelund@...rochip.com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Lars Povlsen <lars.povlsen@...rochip.com>,
        Clément Léger 
        <clement.leger@...tlin.com>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>,
        Kavyasree Kotagiri <kavyasree.kotagiri@...rochip.com>,
        Horatiu Vultur <horatiu.vultur@...rochip.com>
Subject: Re: [PATCH] Revert "reset: microchip-sparx5: allow building as a
 module"

Hi,

Am 2022-07-13 14:08, schrieb Philipp Zabel:
> On Mi, 2022-07-13 at 11:52 +0200, Michael Walle wrote:
>> [+ Horatiu, I missed you earlier, sorry]
>> 
>> Hi Steen,
>> 
>> Am 2022-07-13 11:40, schrieb Steen Hegelund:
>> > I am afraid that the exact list of affected modules is not available,
>> > so using the
>> > RESET_PROT_STAT.SYS_RST_PROT_VCORE bit is the best known way of
>> > resetting as much as possible, and
>> > still continue execution.
>> 
>> Mh, you are designing that chip (at least the LAN966x) no? Shouldn't
>> that information be available anywhere at Microchip? ;)
>> 
>> Anyway, it looks like almost the whole chip is reset
>> except some minor things. So the driver has actually a
>> wrong name. Until recently only the switch driver was the
>> sole user of it (at least on the lan966x). So, my question
>> remains, is this correct? I mean the switch driver says,
>> "reset the switch core", but what actually happens is that
>> the the entire SoC except the CPU and maybe the io mux is reset.
>> What about the watchdog for example? Will that be reset, too?
> 
> If [1-3] are to be trusted, RESET_PROT_STAT[VCORE_RST_PROT_WDT], which
> protects the watchdog from soft reset, is not set by default. So yes?
> 
> There are also AMBA, PCIe, PDBG protection bits against Vcore soft
> reset in this register, depending on the platform.

*But* this also prevents it from reset by the watchdog. I don't know
if we want that?!

I.e. what happens if one sets RESET_PROT_STAT[VCORE_RST_PROT_WDT] and
the watchdog does a reset? OTHO, I guess it is also bad to reset the
watchdog during boot.. IMHO this reset logic doesn't look that well
designed.

> [1] 
> https://microchip-ung.github.io/sparx-5_reginfo/reginfo_sparx-5.html?select=cpu,cpu_regs,reset_prot_stat
> [2] 
> https://microchip-ung.github.io/lan9662_reginfo/reginfo_LAN9662.html?select=cpu,cpu_regs,reset_prot_stat
> [3] 
> https://microchip-ung.github.io/lan9668_reginfo/reginfo_LAN9668.html?select=cpu,cpu_regs,reset_prot_stat

-michael