linux-kernel - Re: [PATCH v3 1/3] mtd: rawnand: denali_dt: add more clocks based on IP datasheet

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Message-ID: <20180622134235.5ab76325@bbrezillon>
Date:   Fri, 22 Jun 2018 13:42:35 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        linux-mtd@...ts.infradead.org,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        David Woodhouse <dwmw2@...radead.org>
Cc:     Mark Rutland <mark.rutland@....com>, devicetree@...r.kernel.org,
        linux-kbuild@...r.kernel.org, Richard Weinberger <richard@....at>,
        linux-kernel@...r.kernel.org,
        "linux-stable #4 . 14+" <stable@...r.kernel.org>,
        Marek Vasut <marek.vasut@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Brian Norris <computersforpeace@...il.com>
Subject: Re: [PATCH v3 1/3] mtd: rawnand: denali_dt: add more clocks based
 on IP datasheet

Hi Masahiro,

On Tue, 19 Jun 2018 13:28:11 +0200
Boris Brezillon <boris.brezillon@...tlin.com> wrote:

> Hi Masahiro,
> 
> On Fri, 15 Jun 2018 10:18:50 +0900
> Masahiro Yamada <yamada.masahiro@...ionext.com> wrote:
> 
> > According to the Denali User's Guide, this IP needs three clocks:
> > 
> >  - clk: controller core clock
> > 
> >  - clk_x: bus interface clock
> > 
> >  - ecc_clk: clock at which ECC circuitry is run
> > 
> > Currently, denali_dt.c requires a single anonymous clock and its
> > frequency.  However, the driver needs to get the frequency of "clk_x"
> > not "clk".  This is confusing because people tend to assume the
> > anonymous clock means the core clock.  In fact, I got a report of
> > SOCFPGA breakage because the timing parameters are calculated based
> > on a wrong frequency.
> > 
> > Instead of the cheesy implementation, the clocks in the real hardware
> > should be represented in the driver and the DT-binding.
> > 
> > However, adding new clocks would break the existing platforms.  For the
> > backward compatibility, the driver still accepts a single clock just as
> > before.  If clk_x is missing, clk_x_rate is set to a hardcoded value.
> > This is fine for existing DT of Socionext UniPhier, and also fixes the
> > issue of Altera (Intel) SOCFPGA because both platforms use 200 MHz for
> > the bus interface clock.
> > 
> > Fixes: 1bb88666775e ("mtd: nand: denali: handle timing parameters by setup_data_interface()")  
> 
> Sorry for changing my mind, but I think this patch is doing more than
> just fixing a bug. The bugfix should IMO be limited to unconditionally
> setting ->clk_x_rate to 200000000 since this is what was done before
> commit 1bb88666775e. And the remaining changes should go in nand/next.

Do you want me to write this patch? Note that I can't really take this
patch since Rob asked for a new version with DT bindings changes placed
in a separate patch.

Regards,

Boris