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

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Date:	Mon, 22 Feb 2016 16:19:39 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Anurag Kumar Vulisha <anurag.kumar.vulisha@...inx.com>
Cc:	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	"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 Monday 22 February 2016 10:53:11 Anurag Kumar Vulisha wrote:
> > >
> > 
> > How would a hardware integrator know which value is right for a particular
> > SoC?
> > 
> > Could it be keyed off the hardware ID? Could the bootloader perhaps set an
> > appropriate value in the AHCI_VEND_PTC register at boot time and the driver
> > read the initial value from it?
> > 
> > From the description, it sounds like this is a policy decision rather than
> > hardware description, and shouldn't really be in here.
> > 
> 
> Thanks for reviewing the patch. Can I use module_param() for this watermark instead of reading it from devicetree or
> doing it in bootloader. In bootloader we are initializing serdes controller for high speed devices. As a part of this initialization
> we will be reseting all the high speed pheripherals which are using serdes, so SATA will also get resetted. Because of this
> reason, can I use module_param() for Rxwatermark value  instead?
> 

I don't know what is appropriate because I have no idea what Rxwatermark
is good for. Can you try describing why we can't just set it to the
correct value for everyone automatically?

	Arnd