Re: [RFC PATCH 2/4] spi: cadence-xspi: add ACMD support for SPI NAND

From: "Nuno Sá" <nuno.sa@analog.com>
To: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Mark Brown <broonie@kernel.org>, Fei Xie <fei.xie@horizon.auto>,
	Richard Weinberger <richard@nod.at>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	Rob Herring <robh@kernel.org>,
	Krzysztof Kozlowski <krzk+dt@kernel.org>,
	Conor Dooley <conor+dt@kernel.org>,
	Parshuram Thombare <pthombar@cadence.com>,
	linux-spi@vger.kernel.org, linux-mtd@lists.infradead.org,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 2/4] spi: cadence-xspi: add ACMD support for SPI NAND
Date: Fri, 25 Sep 2026 12:31:57 +0100	[thread overview]
Message-ID: <arZbZiSTIRT3sxQ2@nsa> (raw)
In-Reply-To: <87ecehljdy.fsf@bootlin.com>

On Fri, Sep 25, 2026 at 12:23:21PM +0200, Miquel Raynal wrote:
> Hello,
> 
> >> > I think that makes sense, that mirrors some ideas people have had for
> >> > optimising SPI mesages in general - submit the sequence to the driver to
> >> > see if it can do it in one, falling back to just running individual
> >> > operations if that doesn't work.  See spi_optimize_message().
> >> 
> >> The spi-mem operation-sequence interface seems very complex to handle
> >> correctly IMHO. I fear such a solution would also require major rewrites
> >> of the core. It is always hard to make fit hardware in code bases not
> >> thought for them. Most of the time being spent in I/Os and wait states,
> >> I am wondering how much would be saved by packing the commands. Do you
> >> have benchmarks?
> >
> > You can see my replies for a more verbose thing, but the TLDR for me was
> > that the gains in performance did not really payed off (vs the
> > complexity we would be adding).
> 
> That's precisely what I was expecting.
> 
> > The real gains
> > for me came by using the nand continuous mode so that using ACMD (and
> > DMA) so that we can actually ready chunks > page size. Of course this works
> > for nand chips supporting cont mode (which hopefully newer ones all do).
> 
> I am very happy to see this feature being used! It already caused quite
> a bit of churn in the core :-)

Yes, I updated my Windbond W25N08LW patch (I resend v2 recently) with
cont mode precisely for this xspi ACMD effort.

- Nuno Sá

> 
> > As for PROGRAM and ERASE commands I really did not saw any added
> > value.
> 
> Yes, most of the time is spent in the wait_ready, which is not getting
> faster with hardware automation.
> 
> > So below is my version of this:
> >
> > https://github.com/analogdevicesinc/linux/pull/3478/changes/477e6095508546552071b825a66522cf697c27c2
> >
> > I pretty much treat NOR and NAND the same thing. Only when you want to
> > do thing like having the controller sending commands itself (or walking
> > pages), then knowing about the chip geometry becomes necessary.
> 
> Thanks,
> Miquèl
> 
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