From mboxrd@z Thu Jan 1 00:00:00 1970
From: daniel.lezcano@linaro.org (Daniel Lezcano)
Date: Wed, 4 Nov 2015 12:19:57 +0100
Subject: [PATCH v2 0/3] let Marvell Berlin SoCs make use of the best delay
timer
In-Reply-To: <4359736.Q4L68M2aRW@wuerfel>
References: <1446560917-6318-1-git-send-email-jszhang@marvell.com>
<5639D409.1030302@linaro.org> <4359736.Q4L68M2aRW@wuerfel>
Message-ID: <5639E9DD.1080309@linaro.org>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org
On 11/04/2015 11:30 AM, Arnd Bergmann wrote:
> 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.
True.
Any ideas / suggestions for an alternative ?
--
Linaro.org ? Open source software for ARM SoCs
Follow Linaro: Facebook |
Twitter |
Blog