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

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Date:	Mon, 22 Feb 2016 10:53:11 +0000
From:	Anurag Kumar Vulisha <anurag.kumar.vulisha@...inx.com>
To:	Arnd Bergmann <arnd@...db.de>
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

Hi Arnd,

> -----Original Message-----
> From: Arnd Bergmann [mailto:arnd@...db.de]
> Sent: Sunday, February 21, 2016 4:05 AM
> To: Anurag Kumar Vulisha
> Cc: robh+dt@...nel.org; pawel.moll@....com; mark.rutland@....com;
> ijc+devicetree@...lion.org.uk; galak@...eaurora.org; tj@...nel.org;
> devicetree@...r.kernel.org; linux-kernel@...r.kernel.org; linux-
> ide@...r.kernel.org; Anirudha Sarangi; Srikanth Vemula; Punnaiah Choudary
> Kalluri; Anurag Kumar Vulisha
> Subject: Re: [RFC PATCH] drivers: ata: Read Rx water mark value from device-
> tree
> 
> On Saturday 20 February 2016 18:48:22 Anurag Kumar Vulisha wrote:
> > index 7ca8b97..7e48dfc 100644
> > --- a/Documentation/devicetree/bindings/ata/ahci-ceva.txt
> > +++ b/Documentation/devicetree/bindings/ata/ahci-ceva.txt
> > @@ -8,6 +8,7 @@ Required properties:
> >
> >  Optional properties:
> >    - ceva,broken-gen2: limit to gen1 speed instead of gen2.
> > +  - ceva,rx-watermark: RX fifo water mark level for SATA controller.
> >
> >  Examples:
> >         ahci@...c0000 {
> > @@ -17,4 +18,5 @@ Examples:
> >                 interrupts = <0 133 4>;
> >                 clocks = <&clkc SATA_CLK_ID>;
> >                 ceva,broken-gen2;
> > +               ceva,rx-watermark = <0x40>;
> >         };
> >
> 
> 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?

Thanks,
Anurag Kumar V
  
> 	Arnd