linux-kernel - Re: [PATCH v2 18/20] mips: csrc-r4k: Decrease r4k-clocksource rating if CPU

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Message-ID: <20200520211200.qhfgdz4qnatyloob@mobilestation>
Date:   Thu, 21 May 2020 00:12:00 +0300
From:   Serge Semin <Sergey.Semin@...kalelectronics.ru>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>
CC:     Serge Semin <fancer.lancer@...il.com>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Paul Burton <paulburton@...nel.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Rob Herring <robh+dt@...nel.org>, <linux-pm@...r.kernel.org>,
        <devicetree@...r.kernel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        <linux-mips@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 18/20] mips: csrc-r4k: Decrease r4k-clocksource rating
 if CPU_FREQ enabled

On Wed, May 20, 2020 at 08:30:57PM +0200, Thomas Bogendoerfer wrote:
> On Wed, May 20, 2020 at 04:48:26PM +0300, Serge Semin wrote:
> > On Wed, May 20, 2020 at 03:38:27PM +0200, Thomas Bogendoerfer wrote:
> > > On Wed, May 20, 2020 at 03:12:01PM +0300, Serge Semin wrote:
> > > > Since you don't like the way I initially fixed it, suppose there we don't have
> > > > another way but to introduce something like CONFIG_MIPS_CPS_NS16550_WIDTH
> > > > parameter to select a proper accessors, like sw in our case, and sb by defaul).
> > > > Right?
> > > 
> > > to be on the safe side it's probably the best thing. But I don't know
> > > enough about CPS_NS16550 to judge whether shift value correlates with
> > > possible access width.
> > 
> > The base address passed to the _mips_cps_putc() leaf is UART-base address. It
> > has nothing to do with CPS. See:
> 
> ok, I'm confused. So this isn't an uart inside CPS hardware, but an uart used
> by CPS code for debug output, right ? 

Right. It's not CPS, but just UART available on the system. See a comment in the
arch/mips/kernel/cps-vec-ns16550.S:
/**
 * mips_cps_bev_dump() - dump relevant exception state to UART
 * @a0: pointer to NULL-terminated ASCII string naming the exception
 *
 * Write information that may be useful in debugging an exception to the
 * UART configured by CONFIG_MIPS_CPS_NS16550_*.
 *...
 */
LEAF(mips_cps_bev_dump)
        move            s0, ra
        move            s1, a0

        li              t9, CKSEG1ADDR(CONFIG_MIPS_CPS_NS16550_BASE)
        ...

See the base is just loaded to the t9 register.

> 
> To solve the issued please add CONFIG_MIPS_CPS_NS16550_WIDTH to select the
> correct access width.

Ok. Thanks.

-Sergey

> 
> Thomas.
> 
> -- 
> Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
> good idea.                                                [ RFC1925, 2.3 ]