Re: [PATCH 2/5] mtd: rawnand: qcom: Add initial support for qspi nand

From: Miquel Raynal <miquel.raynal@bootlin.com>
To: Md Sadre Alam <quic_mdalam@quicinc.com>
Cc: Boris Brezillon <boris.brezillon@collabora.com>,
	<linux-kernel@vger.kernel.org>, <devicetree@vger.kernel.org>,
	<linux-mtd@lists.infradead.org>, <linux-arm-msm@vger.kernel.org>,
	<robh+dt@kernel.org>, <vigneshr@ti.com>, <richard@nod.at>,
	<agross@kernel.org>, <bjorn.andersson@linaro.org>,
	<quic_srichara@quicinc.com>, <qpic_varada@quicinc.com>,
	<quic_sjaganat@quicinc.com>
Subject: Re: [PATCH 2/5] mtd: rawnand: qcom: Add initial support for qspi nand
Date: Mon, 6 Mar 2023 15:38:51 +0100	[thread overview]
Message-ID: <20230306153851.0dcdda27@xps-13> (raw)
In-Reply-To: <b70ddb40-a1f1-f967-6b7b-057a39b0bcc2@quicinc.com>

Hello,

quic_mdalam@quicinc.com wrote on Mon, 6 Mar 2023 19:45:58 +0530:

> On 10/29/2020 2:37 PM, Boris Brezillon wrote:
> > Hello,
> >
> > On Sat, 10 Oct 2020 11:01:39 +0530
> > Md Sadre Alam <mdalam@codeaurora.org> wrote:
> >  
> >> This change will add initial support for qspi (serial nand).
> >>
> >> QPIC Version v.2.0 onwards supports serial nand as well so this
> >> change will initialize all required register to enable qspi (serial
> >> nand).
> >>
> >> This change is supporting very basic functionality of qspi nand flash.
> >>
> >> 1. Reset device (Reset QSPI NAND device).
> >>
> >> 2. Device detection (Read id QSPI NAND device).  
> > Unfortunately, that's not going to work in the long term. You're
> > basically hacking the raw NAND framework to make SPI NANDs fit. I do
> > understand the rationale behind this decision (re-using the code for
> > ECC and probably other things), but that's not going to work. So I'd
> > recommend doing the following instead:
> >
> > 1/ implement a SPI-mem controller driver
> > 2/ implement an ECC engine driver so the ECC logic can be shared
> >     between the SPI controller and raw NAND controller drivers
> > 3/ convert the raw NAND driver to the exec_op() interface (none of
> >     this hack would have been possible if the driver was using the new
> >     API)
> >
> > Regards,
> >
> > Boris
> >  
>     Sorry for late reply, again started working on this feature support.  The QPIC v2 on wards there is serial nand support got added , its not a standard SPI controller
> 
>     its QPIC controller having support for serial nand. All SPI related configuration done by QPIC hardware and its not exposed as SPI bus to the external world. Only based on
> 
>     QPIC_SPI_CFG = 1, serial functionality will get selected. So that no need to implement as SPI-mem controller driver, since its not a SPI controller.
> 
>    Please check the below diagram for top view of QPIC controller.

One of the hard things in the Linux kernel is to make devices fit
frameworks. This feature does not fit the raw NAND framework. It does
not follow any of the conventions taken there. It is not gonna be
accepted there. You need to expose spi-mem functionalities, even if the
spi-proper features are not available. I believe your situation still
fits the spi-mem abstraction.

Thanks,
Miquèl

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