From: Arnd Bergmann <arnd@arndb.de>
To: Michal Simek <michal.simek@xilinx.com>
Cc: "Anurag Kumar Vulisha" <anuragku@xilinx.com>,
"Rob Herring" <robh@kernel.org>,
"Sören Brinkmann" <soren.brinkmann@xilinx.com>,
"pawel.moll@arm.com" <pawel.moll@arm.com>,
"mark.rutland@arm.com" <mark.rutland@arm.com>,
"ijc+devicetree@hellion.org.uk" <ijc+devicetree@hellion.org.uk>,
"galak@codeaurora.org" <galak@codeaurora.org>,
"tj@kernel.org" <tj@kernel.org>,
"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-ide@vger.kernel.org" <linux-ide@vger.kernel.org>,
"Anirudha Sarangi" <anirudh@xilinx.com>,
"Srikanth Vemula" <svemula@xilinx.com>,
"Punnaiah Choudary Kalluri" <punnaia@xilinx.com>
Subject: Re: [RFC PATCH] drivers: ata: Read Rx water mark value from device-tree
Date: Wed, 02 Mar 2016 10:11:06 +0100 [thread overview]
Message-ID: <3012728.7zDNPtQ7kR@wuerfel> (raw)
In-Reply-To: <56D69EDD.40400@xilinx.com>
On Wednesday 02 March 2016 09:05:49 Michal Simek wrote:
> On 2.3.2016 06:53, Anurag Kumar Vulisha wrote:
> >>>>>
> >>>>> I would probably make this dependent on the compatible string
> >>>>> instead, and have a table in the device driver that uses a
> >>>>> specific value for each variant of the device, but either way should be
> >> fine.
> >>>>>
> >>>>> Having a separate property is most appropriate if for each
> >>>>> hardware revision there is exactly one ideal value, while a table
> >>>>> in the driver makes more sense if this takes a bit of tuning and
> >>>>> the driver might choose to optimize it differently based on other
> >>>>> constraints, such as its own interrupt handler implementation.
>
> that 0x40 is value choose based on testing that it is not causing any
> visible problem and this is used as default value in the driver
> (PTC_RX_WM_VAL - ahci_ceva.c)
>
> Values which you can setup are in range 0x0 - 0x7f (7bits). It means
> hardware fifo size is probably 0x80.
>
> And this dt/module parameter is IMHO just sw setting setup by user.
> It means I am not quite sure that this is DT parameter because it is
> just SW setting.
> I expect this range will be valid for all silicon revisions.
> If happen that any silicon revision can't setup certain level because of
> HW bug we can handle it via DT parameter or specific compatible string.
> But setting up watermark SW level via DT doesn't look correct to me.
>
> Please let me know what you think.
Ok, thanks for the background. I think we should just leave it to be
set by the driver then. Please make sure that each SoC specific .dtsi
file has a unique "compatible" string for the device though, so that
the driver can later override it based on the specific variant if
that ends up being necessary for performance or bug-avoidance.
Arnd
next prev parent reply other threads:[~2016-03-02 9:11 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-20 13:18 [RFC PATCH] drivers: ata: Read Rx water mark value from device-tree Anurag Kumar Vulisha
2016-02-20 22:34 ` Arnd Bergmann
2016-02-22 10:53 ` Anurag Kumar Vulisha
2016-02-22 15:19 ` Arnd Bergmann
2016-02-23 5:58 ` Anurag Kumar Vulisha
2016-02-23 10:20 ` Arnd Bergmann
2016-02-23 15:29 ` Anurag Kumar Vulisha
[not found] ` <3802E9A6666DF54886E2B9CBF743BA9825E0117F-4lKfpRxZ5enZMOc0yg5rMog+Gb3gawCHQz34XiSyOiE@public.gmane.org>
2016-02-23 19:29 ` Rob Herring
2016-02-26 13:48 ` Anurag Kumar Vulisha
2016-03-02 5:53 ` Anurag Kumar Vulisha
2016-03-02 8:05 ` Michal Simek
2016-03-02 9:11 ` Arnd Bergmann [this message]
2016-03-02 9:27 ` Michal Simek
2016-03-02 11:42 ` Arnd Bergmann
2016-03-02 11:51 ` Michal Simek
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