linux-kernel - Re: [RFC PATCH] drivers: ata: Read Rx water mark value from device-tree

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Date:	Wed, 2 Mar 2016 12:51:44 +0100
From:	Michal Simek <michal.simek@...inx.com>
To:	Arnd Bergmann <arnd@...db.de>,
	Michal Simek <michal.simek@...inx.com>
CC:	Anurag Kumar Vulisha <anuragku@...inx.com>,
	Rob Herring <robh@...nel.org>,
	Sören Brinkmann <soren.brinkmann@...inx.com>,
	"pawel.moll@....com" <pawel.moll@....com>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	"galak@...eaurora.org" <galak@...eaurora.org>,
	"tj@...nel.org" <tj@...nel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	Anirudha Sarangi <anirudh@...inx.com>,
	Srikanth Vemula <svemula@...inx.com>,
	"Punnaiah Choudary Kalluri" <punnaia@...inx.com>
Subject: Re: [RFC PATCH] drivers: ata: Read Rx water mark value from
 device-tree

On 2.3.2016 12:42, Arnd Bergmann wrote:
> On Wednesday 02 March 2016 10:27:51 Michal Simek wrote:
>>
>> No problem with default value in driver. Something has to be setup.
>> Reset value based on reg spec I was checking is 0x20. Based on our
>> testing we saw some issues that's why 0x40 was setup as default value.
>> There is a need to be able to configure this value for example for
>> testing different values that's why I think module parameter should be
>> the right way to go.
> 
> I don't object to the module parameter, but I don't understand how important
> that kind of testing is to normal users. Who would set it, aside from
> the person writing that driver to come up with the correct default?
> 
>> If this should be DT parameters there should be different ceva IP which
>> allows different fifo size and different watermark level to be setup by
>> user.
>>
>> What do you think? Does it sound reasonable.
> 
> Having a property for the actual hardware fifo size once you get
> different implementations seems like the correct approach, but it's
> moot as long as all implementations are hardwired to 128 entries.

yep right now and we don't know what can happen in future. I just wanted
to point to example where this property can be specified or wired to
particular compatible string.

Anurag: Please make it as module parameter instead of DT parameter.

Thanks,
Michal