From: Arnd Bergmann <arnd@arndb.de>
To: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Jisheng Zhang <jszhang@marvell.com>,
tglx@linutronix.de, linux@arm.linux.org.uk,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 0/3] let Marvell Berlin SoCs make use of the best delay timer
Date: Wed, 04 Nov 2015 11:30:43 +0100 [thread overview]
Message-ID: <4359736.Q4L68M2aRW@wuerfel> (raw)
In-Reply-To: <5639D409.1030302@linaro.org>
On Wednesday 04 November 2015 10:46:49 Daniel Lezcano wrote:
> On 11/03/2015 03:28 PM, Jisheng Zhang wrote:
> > In case there are several possible delay timers, we purely base the
> > selection on the frequency, which is suboptimal in some cases. Take
> > one Marvell Berlin platform for example: we have arch timer and dw-apb
> > timer. The arch timer freq is 25MHZ while the dw-apb timer freq is
> > 100MHZ, current selection would choose the dw-apb timer. But the dw
> > apb timer is on the APB bus while arch timer sits in CPU, the cost
> > of accessing the apb timer is higher than the arch timer.
> >
> > This series firstly modifies register_current_timer_delay() to choose
> > the highest rating delay timer: use the rating as a primary indication
> > and fall back to comparing the frequency if the rating is not set or
> > the same. Then we set the arch_delay_timer rating as 400, finally
> > Implement ARM delay timer for the dw_apb_timer and set its rating as 300.
>
> Hi Jisheng, Arnd,
>
> I don't feel comfortable with the rating / freq think. I am afraid this
> approach based on heuristic will bring a lot of complexity and
> workarounds in the code for a small benefit.
>
> Why don't we define a DT entry for the delay timer ? So we delegate the
> choice to the platform DT definition.
That would be wrong, because the fact that Linux uses a timer to
optimize its udelay() function is not a feature of the hardware.
Arnd
next prev parent reply other threads:[~2015-11-04 10:31 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-03 14:28 [PATCH v2 0/3] let Marvell Berlin SoCs make use of the best delay timer Jisheng Zhang
2015-11-03 14:28 ` [PATCH v2 1/3] ARM: delay: choose the highest rating " Jisheng Zhang
2015-11-03 14:28 ` [PATCH v2 2/3] ARM: arch_timer: set the arch_delay_timer rating as 400 Jisheng Zhang
2015-11-03 14:28 ` [PATCH v2 3/3] clocksource/drivers/dw_apb_timer_of: Implement ARM delay timer Jisheng Zhang
2015-11-04 9:46 ` [PATCH v2 0/3] let Marvell Berlin SoCs make use of the best " Daniel Lezcano
2015-11-04 10:30 ` Arnd Bergmann [this message]
2015-11-04 11:19 ` Daniel Lezcano
2015-11-04 12:19 ` Arnd Bergmann
2015-11-05 2:36 ` Jisheng Zhang
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