linux-kernel - RE: [PATCH v2 2/3] soc: sifive: Add SiFive specific Cadence DDR controller driver

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Message-ID: <CH2PR07MB71904C52A6BD735852151418CD3E0@CH2PR07MB7190.namprd07.prod.outlook.com>
Date:   Thu, 17 Sep 2020 09:56:30 +0000
From:   Dhananjay Vilasrao Kangude <dkangude@...ence.com>
To:     Palmer Dabbelt <palmer@...belt.com>,
        Christoph Hellwig <hch@...radead.org>
CC:     "yash.shah@...ive.com" <yash.shah@...ive.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "aou@...s.berkeley.edu" <aou@...s.berkeley.edu>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "sachin.ghadi@...ive.com" <sachin.ghadi@...ive.com>,
        "rrichter@...vell.com" <rrichter@...vell.com>,
        "james.morse@....com" <james.morse@....com>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>
Subject: RE: [PATCH v2 2/3] soc: sifive: Add SiFive specific Cadence DDR
 controller driver



> -----Original Message-----
> From: Palmer Dabbelt <palmer@...belt.com>
> Sent: Wednesday, September 9, 2020 8:42 AM
> To: Christoph Hellwig <hch@...radead.org>; Dhananjay Vilasrao Kangude
> <dkangude@...ence.com>
> Cc: yash.shah@...ive.com; robh+dt@...nel.org; Paul Walmsley
> <paul.walmsley@...ive.com>; bp@...en8.de; mchehab@...nel.org;
> tony.luck@...el.com; devicetree@...r.kernel.org; aou@...s.berkeley.edu;
> linux-kernel@...r.kernel.org; sachin.ghadi@...ive.com;
> rrichter@...vell.com; james.morse@....com; linux-
> riscv@...ts.infradead.org; linux-edac@...r.kernel.org
> Subject: Re: [PATCH v2 2/3] soc: sifive: Add SiFive specific Cadence DDR
> controller driver
> 
> EXTERNAL MAIL
> 
> 
> On Sun, 06 Sep 2020 23:11:26 PDT (-0700), Christoph Hellwig wrote:
> > On Mon, Sep 07, 2020 at 11:17:58AM +0530, Yash Shah wrote:
> >> Add a driver to manage the Cadence DDR controller present on SiFive
> >> SoCs At present the driver manages the EDAC feature of the DDR
> controller.
> >> Additional features may be added to the driver in future to control
> >> other aspects of the DDR controller.
> >
> > So if this is a generic(ish) Cadence IP block shouldn't it be named
> > Cadence and made generic?  Or is the frontend somehow SiFive specific?
> 
> For some reason I thought we had a SiFive-specific interface to this, but I may
> have gotten that confused with something else as it's been a while.  Someone
> from SiFive would probably have a better idea, but it looks like the person I'd
> ask isn't thereany more so I'm all out of options ;)
> 
> It looks like there was a very similar driver posted by Dhananjay Kangude
> from Cadence in April:
> https://urldefense.com/v3/__https://lkml.org/lkml/2020/4/6/358__;!!EHscm
> S1ygiU1lA!UfVYWzQqCgaUNKN156ffKM5NkFoYtPhHapruC3yqme7nvbUBnD2
> mEHg8F6it4y4$  .  Some of the register definitions seem to be different, but
> the code I looked at is very similar so there's at least some bits that could be
> shared.  I found a v4 of that patch set, but that was back in May:
> https://urldefense.com/v3/__https://lkml.org/lkml/2020/5/11/912__;!!EHsc
> mS1ygiU1lA!UfVYWzQqCgaUNKN156ffKM5NkFoYtPhHapruC3yqme7nvbUBnD
> 2mEHg8DeCwApk$  .  It alludes to a v5, but I can't find one.  I've added
> Dhananjay, maybe he knows what's up?
> 
> I don't know enough about the block to know if the subtle difference in
> register names/offsets means.  They look properly jumbled up (ie, not just an
> offset), so maybe there's just different versions or that's the SiFive-specific
> part I had bouncing around my head?  Either way, it seems like one driver
> with some simple configuration could handle both of these -- either sticking
> the offsets in the DT (if they're going to be different everywhere) or by
> coming up with some version sort of thing (if there's a handful of these).
> 
> I'm now also a bit worried about the provenace of this code.  The two drivers
> are errily similar -- for example, the variable definitions in handle_ce()
> 
>        u64 err_c_addr = 0x0;
>        u64 err_c_data = 0x0;
>        u32 err_c_synd, err_c_id;
>        u32 sig_val_l, sig_val_h;
> 
> are exactly the same.
[Dhananjay Kangude]
 Hi Palmer,
       	Sorry for delayed reply.
	I was expecting new changes into the hardware IP since last couple of
months thus I haven't up streamed V5 patch till now. The cadence driver version 
is of more generic for cadence DDR controllers which could be part of other SoCs too.
I would suggest Yash to patch Sifive specific changes once cadence DDR controller driver 
get up streamed. I will send V5 in coming days.

Thank,
Dhananjay