linux-kernel - Re: [PATCH] riscv: dts: allwinner: d1: Add SPI0 controller node

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Date:   Fri, 5 May 2023 17:00:15 +0100
From:   Andre Przywara <andre.przywara@....com>
To:     Maxim Kiselev <bigunclemax@...il.com>
Cc:     robh+dt@...nel.org,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Samuel Holland <samuel@...lland.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Cristian Ciocaltea <cristian.ciocaltea@...labora.com>,
        devicetree@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv: dts: allwinner: d1: Add SPI0 controller node

On Fri, 5 May 2023 17:27:07 +0400
Maxim Kiselev <bigunclemax@...il.com> wrote:

Hi Maxim,

> > From a quick glance at the manuals, it
> > looks like there are not quite the same, though: the D1/R528/T113s
> > mentions a SPI_SAMP_DL register @0x28, whereas the older IP has a SPI_CCR
> > register @0x24 - which is not mentioned in the newer manuals. The driver
> > relies on that clock control register, so it wouldn't really work
> > reliably, if that register is not there.  
> 
> Thank you for pointing this out. I missed this difference.
> I actually have a board with T113 SoC, and it looks like writing to
> SPI_CCR@...4 does nothing.

According to the manual, the register doesn't exist, so this would support
this theory. Most Allwinner IP just implements non-existing registers as
RAZ/WI.

> And it doesn't affect access to connected SPI NOR flash (read\write
> operations are fine).

I guess it just works with *some* (default?) clock settings then. Might be
faster than configured, but the SPI flash chip might be fine with that.

> But I completely agree with you that this difference should be handled
> by the spi driver.

As Samuel pointed out on IRC, there are patches, for the R329, using the
same IP:
https://lore.kernel.org/lkml/BYAPR20MB2472E8B10BFEF75E7950BBC0BCF79@BYAPR20MB2472.namprd20.prod.outlook.com/
And he also seemed to have issues, at least with SPI-NAND on one board:
https://lore.kernel.org/lkml/0b5b586a-3bc7-384e-103c-e40d0b2fac23@sholland.org/

Can you please try these patches, and use:
compatible = "allwinner,sun20i-d1-spi", "allwinner,sun50i-r329-spi";
for the compatible string?
If possible, you could revive this series, and add the D1/T113s support on
top: just add the compatible string combo to the binding document.

Cheers,
Andre