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bh=bwV59Poqvr4TETkpzfKMM8Wo2Gkh86LU/Q3T3dW528g=; b=d89o6SPV3H8UwGn6tgVBA2/mYk+pxDiQAuMzVnhJM36IBfoxayPN3cWwAbKYoiXDBLzgGs 6YFdxEIuw0wWd+bdS6rbXC3DDWSTGWvsMX5LbNUWN3BHtvYlgltchwOoaIifHyJEMD9zEU 34CxwQXoPwOLh1c59fEdszpQB/rFWdiaIAvglgrGWeMm+Lb+AWF9tsGaLXDuxJ70qBEq0B 2vFBpgbUhVoX2J8xuayyuhU5NKydMAmSrvsahoBAlvbITuXBgsAQZAOg5Rp0x8QeD7dp9Y 3q5pKQaPhX0kepssvyQBErbERYG+HixhosZNBonmXOgcg3N22rEc0pxg5QJLfg== From: Miquel Raynal To: "Michael Walle" Cc: "Santhosh Kumar K" , "Pratyush Yadav" , , , , , , , , , , , Subject: Re: [RFC PATCH 01/10] spi: spi-mem: Introduce support for tuning controller In-Reply-To: (Michael Walle's message of "Wed, 03 Dec 2025 10:28:23 +0100") References: <20250811193219.731851-1-s-k6@ti.com> <20250811193219.731851-2-s-k6@ti.com> <87seguemzu.fsf@bootlin.com> User-Agent: mu4e 1.12.7; emacs 30.2 Date: Wed, 03 Dec 2025 10:50:12 +0100 Message-ID: <87jyz3ao8b.fsf@bootlin.com> Precedence: bulk X-Mailing-List: linux-spi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Last-TLS-Session-Version: TLSv1.3 >>> I think we should start with the requirement to have the pattern flashed >>> already and figure out how SPI NOR or SPI NAND can discover that >>> (perhaps via NVMEM?). > > But we should also keep in mind that certain flashes might return > tuning data during the dummy cycles. I.e. the PHY might probably be > tuned on each read and there is no need for any pre-programmed > pattern. > > I'm not saying it should be implemented, but the current > implementation should be that flexible that it will be easy to add > that later. Conceptually, yes, but in practice, I know no controller capable of using just a few cycles every transfer to calibrate themselves automatically and reaching such an optimized speed state as the cadence controller is capable of ATM. Despite the end result being close, I would still consider this other way to optimize the I/Os somewhat orthogonal. If someone has some knowledge to share about the training patterns sent during the dummy cycles, I am all ears though. >> For SPI NOR, we do not have an equivalent "write-to-cache" possible, so >> we still require a pre-flashed pattern region. At the moment this is >> provided via a dedicated "phypattern" partition, and its offset is >> obtained through the of_get_* APIs. >> >> Regarding ways to locate the partition: >> >> 1. Using NVMEM: >> a. Exposing the phypattern partition as an NVMEM cell and issuing an >> NVMEM read during tuning does not work reliably, because NVMEM >> ends up calling into the MTD read path and we cannot control which >> read_op variant is used for the read. >> >> b. Advertising the partition as an NVMEM cell and using NVMEM only >> to fetch the offset is not possible either. NVMEM abstracts the >> private data, including partition offsets, so we can't retrieve >> the offset as well. > > You can probably extend the NVMEM API in some way - or switching the > read_op on the fly. > >> 2. Using of_get_* APIs: >> Using the standard OF helpers to locate the phypattern partition >> and retrieve its offset is both reliable and straighforward, and >> is the approach currently implemented in v2. > > I don't like that hardcoded partition name which is basically > becoming an ABI then. > > At least we'd need some kind of phandle to the partition inside the > controller node (and get the ACK from the DT maintainers). Yes, agreed, this is controller specific, if we need to use an of_ API (which is still not needed for SPI NANDs, only for tuning the read SPI NOR path), it should not just be a partition hardcoded name but a phandle in the controller node. Thanks, Miqu=C3=A8l