Re: [PATCH v2 18/20] mips: csrc-r4k: Decrease r4k-clocksource rating if CPU_FREQ enabled

From: Serge Semin <Sergey.Semin@baikalelectronics.ru>
To: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Serge Semin <fancer.lancer@gmail.com>,
	Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>,
	Paul Burton <paulburton@kernel.org>,
	Ralf Baechle <ralf@linux-mips.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Arnd Bergmann <arnd@arndb.de>, Rob Herring <robh+dt@kernel.org>,
	<linux-pm@vger.kernel.org>, <devicetree@vger.kernel.org>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	<linux-mips@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 18/20] mips: csrc-r4k: Decrease r4k-clocksource rating if CPU_FREQ enabled
Date: Wed, 20 May 2020 15:12:01 +0300	[thread overview]
Message-ID: <20200520121201.wohv6u646rx5otkf@mobilestation> (raw)
In-Reply-To: <20200519155053.GB15797@alpha.franken.de>

On Tue, May 19, 2020 at 05:50:53PM +0200, Thomas Bogendoerfer wrote:
> On Mon, May 18, 2020 at 11:57:52PM +0300, Serge Semin wrote:
> > On Mon, May 18, 2020 at 06:32:06PM +0200, Thomas Bogendoerfer wrote:
> > > On Mon, May 18, 2020 at 04:48:20PM +0300, Serge Semin wrote:
> > > > On Fri, May 15, 2020 at 11:06:47PM +0200, Thomas Bogendoerfer wrote:
> > > > > On Fri, May 15, 2020 at 10:48:27AM +0300, Serge Semin wrote:
> > > > > > Thomas,
> > > > > > Could you take a look at my comment below so I could proceed with the
> > > > > > patchset v3 development?
> > > > > 
> > > > > I can't help, but using r4k clocksource with changing frequency is
> > > > > probaly only usefull as a random generator. So IMHO the only two
> > > > > options are disabling it or implement what arch/x86/kernel/tsc.c does.
> > > > > 
> > > > > Thomas.
> > > > 
> > > > Thomas, could you proceed with the rest of the patches review?
> > > > ├─>[PATCH v2 16/20] bus: cdmm: Add MIPS R5 arch support
> > > > ├─>[PATCH v2 15/20] mips: cdmm: Add mti,mips-cdmm dtb node support
> > > 
> > > both are not my call, but look ok to me.
> > 
> > Can I add your Reviewed-by tag there then?
> 
> only for 16/20. 15/20 looks ok to me, but I have not enough insides
> on the hardware to say this is good.
> 
> > > > ├─>[PATCH v2 13/20] mips: early_printk_8250: Use offset-sized IO-mem accessors
> > > 
> > > that's broken. A reg shift of 2 doesn't mean we could use 32bit access
> > > to the registers on other platforms. As I don't think adding some ifdefery
> > > makes things nicer, just implement the your prom_putchar in board code.
> > 
> > I thought about that initially, but then I decided to alter the generic
> > early_printk_8250 code instead. My version of prom_putchar() would be almost
> > the same as one implemented in the early_printk_8250 module except minor
> > modification of replacing readb/writeb methods with readl/writel. So I didn't
> > want to duplicate the code, but wanted to provide a general way to fix the
> > problem potentially also for another platforms.
> > 
> > Since you don't like this fix alternatively I'd suggest to add the reg_width
> > parameter passed to the setup_8250_early_printk_port() method like this:
> > -setup_8250_early_printk_port(unsigned long base, unsigned int reg_shift,
> > -                             unsigned int timeout)
> > +setup_8250_early_printk_port(unsigned long base, unsigned int reg_shift,
> > +                             unsigned int reg_width, unsigned int timeout)
> > 
> > By reg_width parameter we could determine the actual width of the register:
> >  static inline u8 serial_in(int offset)
> >  {
> > -       return readb(serial8250_base + (offset << serial8250_reg_shift));
> > +       u8 ret = 0xFF;
> > +
> > +       offset <<= serial8250_reg_shift;
> > +       switch (serial8250_reg_width) {
> > +       case 1:
> > +               ret = readb(serial8250_base + offset);
> > +               break;
> > +       case 2:
> > +               ret = readw(serial8250_base + offset);
> > +               break;
> > +       case 4:
> > +               ret = readl(serial8250_base + offset);
> > +               break;
> > +       default:
> > +               break;
> > +       }
> > +
> > +       return ret;
> >  }
> > 
> > The similar modification will be implemented for serial_out(). I'll also modify
> 
> look at the lines of code you are adding. Doing your own prom_putchar will
> probably have less lines.
> 
> > What do you think about this?
> 
> please do your own prom_putchar.

One more time regarding this problem but in appliance to another part of the
MIPS code. I've missed the patch to draw your attention to:
[PATCH v2 14/20] mips: Use offset-sized IO-mem accessors in CPS debug printout

There I've applied the same fix as in the patch:
[PATCH v2 13/20] mips: early_printk_8250: Use offset-sized IO-mem accessors

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?

(Note UART_L is incorrectly created in that patch, I'll remove that macro in
v3.)

-Sergey

> 
> 
> > > 
> > > > ├─>[PATCH v2 12/20] mips: MAAR: Add XPA mode support
> > > 
> > > looks ok so far.
> > 
> > Can I add your Reviewed-by tag there then?
> 
> As I'm the maintainer of the part, I've simply applied it.
> 
> > > 
> > > > ├─>[PATCH v2 10/20] mips: Add CONFIG/CONFIG6/Cause reg fields macro
> > > 
> > > that is fine
> > 
> > Can I add your Reviewed-by tag there then?
> 
> As this didn't apply cleanly, I'll apply it after you've resent it.
> IMHO no need for a Reviewed-by.
> 
> > > > └─>[PATCH v2 09/20] mips: Add CP0 Write Merge config support
> > > 
> > > this is IMHO a dangerous change. Enabling write merging for any
> > > CPU supporting it might triggers bugs. Do it in your board bringup
> > > code and at the moment I don't see a reason for the rest of that
> > > patch.
> > 
> > Let's at least leave the mm_config() implementation but without the write-merge
> > enabling by default. Providing features availability macro
> > cpu_has_mm_sysad/cpu_has_mm_full and c0 config fields
> 
> do you have a user of that ? I'm not introducing code nobody uses.
> 
> > I could use them to implement a code pattern like:
> > 
> > +	if (cpu_has_mm_full) {
> > +		unsigned int config0 = read_c0_config();
> > +               config0 = (config0 & ~MIPS_CONF_MM) | MIPS_CONF_MM_FULL;
> > +               write_c0_config(config0);
> > +	}
> 
> you know you are running on a R5 core, so you know you have MM_FULL.
> No need to check this.
> 
> > By doing so I can manually enable/disable the MM feature in the
> > cpu-feature-overrides.h. Without that I'd have to locally define these macro,
> > which isn't good seeing they are in fact generic and can be useful for other
> > platforms with SYSAD and FULL MM feature available. What do you think?
> 
> To me this is a hardware feature I expect to be done by firmware and
> Linux shouldn't care about it, if it doesn't have any software
> implications.
> 
> Thomas.
> 
> -- 
> Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
> good idea.                                                [ RFC1925, 2.3 ]