linux-kernel - Re: [PATCH] ARM: dts: keystone: use one to one address translations under netcp

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Date:	Thu, 3 Sep 2015 15:18:16 -0400
From:	Murali Karicheri <m-karicheri2@...com>
To:	Tony Lindgren <tony@...mide.com>,
	santosh shilimkar <santosh.shilimkar@...cle.com>
CC:	"Kwok, WingMan" <w-kwok2@...com>,
	"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>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"ssantosh@...nel.org" <ssantosh@...nel.org>
Subject: Re: [PATCH] ARM: dts: keystone: use one to one address translations
 under netcp

Tony,
On 09/03/2015 10:26 AM, Tony Lindgren wrote:
> * santosh shilimkar <santosh.shilimkar@...cle.com> [150902 08:55]:
>>
>> I suspected the same. I know back then we started with SERDES code
>> with NETCP but as you already know, its a separate block which
>> is needed for NIC card to work. Its more of phy and hence its
>> having different address space is not surprising.
>
> The point Santosh is making here though is that any drivers
> tinkering with registers belonging to a separate hardware block
> is a recipe for a long term maintenance nightmare with mysterious

That is what we want to avoid as well. If I interpret your statement 
correctly, you don't want SerDes driver update the register of say 
SGMII, right? But we will have to based on the hardware design. So it 
can't be a standalone device driver IMO and it has to be part of the 
respective peripheral device driver.

> bugs popping up as things are not clocked or powered properly
> or become racy with other drivers.
>
> Each hardware block needs to have it's own driver and then the
> drivers can communicate using some Linux generic APIs like clock,
> regulator, phy, or mailbox frameworks.

That depends on what your definition of a hardware block is. Inside 
NetCP, there are many hardware blocks that work together to provide the 
NIC functionality, and SerDes is one of them. Where ever possible, we 
have separate drivers :- knav qmss, knav pkt dma, ethss, mdio etc. Ethss 
driver manages Eth subsystem that includes SGMII and SerDes. 
Unfortunately SerDes is tightly integrated with ethss and taking it out 
as a separate driver (Say Phy) is not a good idea. We will posting an 
RFC for this soon and probably we can discuss it more then.

Probably we will fold this into the RFC series to give this a better 
context.

Murali

>
> Regards,
>
> Tony
>

-- 
Murali Karicheri
Linux Kernel, Keystone
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