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bh=/Imw93ygjLS91BX1TYQywEnwPobZLvvLSfN2yGVqTa8=; b=NUGOt2qjI0L9+6HoPSM4LgZhESsfIeMdnzahBizANCDctJp73VqtmCphDg2+KQak+ZT4c9 1BXOkH3PiXfSer7FuJ3PKRSSkLm7hkUNi3ehN2clm1j/fRMDaM9M09VyC/IYllnwi9bjvx 0NE5el19DmMVvEtLAhC3a6nocVh6Mse3BVG8AERs0viJ7HfRu35w4bMiiHqeYuIA7/CeXe k3T5OeAda+fYO526blJDuaSKAqqg+bfb0fsTH0UkdPIZxssWnv3ui1Iy8JdHiJVRLLKLRQ ivt6MhCoP6ncTBQ8VbPzM8f62ifHQ/X9MJqwXa/438gYFKkpebEEkgBIJOQwJg== From: Miquel Raynal To: Santhosh Kumar K Cc: Mark Brown , Richard Weinberger , "Vignesh Raghavendra" , Thomas Petazzoni , , , , , , , Subject: Re: [PATCH RFC 0/4] mtd/spi-mem: Enable DQS support In-Reply-To: <41f49187-e68b-4731-ac86-7c346de63173@ti.com> (Santhosh Kumar K.'s message of "Sat, 7 Feb 2026 01:02:12 +0530") References: <20260205-winbond-nand-next-phy-tuning-v1-0-5e7d3976f0f1@bootlin.com> <41f49187-e68b-4731-ac86-7c346de63173@ti.com> User-Agent: mu4e 1.12.7; emacs 30.2 Date: Tue, 10 Feb 2026 11:23:55 +0100 Message-ID: <87pl6czykk.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 On 07/02/2026 at 01:02:12 +0530, Santhosh Kumar K wrote: > Hello Miquel, > > On 06/02/26 00:36, Miquel Raynal wrote: >> For his PHY tuning series on the Cadence QSPI controller embedded in TI >> SoCs, Santhosh needs to access the availability of the DQS (data strobe) >> signal. This is a chip dependent capability, which may sometimes be >> enabled. >> Create a SPI memory flag for it, let the SPI NAND core set this flag >> when it knows about the capability, and show how to use it from a SPI >> controller driver. >> This is an alternative at needing a DT property. Please note that >> there >> are a few blind spots: >> - the line may not be wired (this would be surprising, but can be >> flagged this time by a DT property) >> - manufacturer drivers must enable the feature if it is >> available (especially for high speed DTR modes) >> - this implementation is proposed for SPI NANDs only, if this proposal >> is accepted the same approach must be taken in SPI NOR. > > Thank you for the series! > > As mentioned in the tuning series, in addition to the flash advertising > its DQS capability, we also need a DT property to describe whether DQS > is physically connected to the controller. This can be represented using > either a "dqs-wired" or "dqs-not-wired" property; the exact naming can > be chosen based on the majority case. > > With this series, the controller will enable or disable DQS by logically > AND-ing both pieces of information. Do we really need this? My expectation is that someone wiring an octal DTR SPI chip for high speed octal DTR use **will** route the DQS signal. If this signal is not wired, I want to consider this as a hardware bug. As a result, the default case should be "if there is a DQS signal, use it". If, however people come up with non correctly routed chips but still want high frequency support, the burden will be on them to ask for a DT property describing a non compliant hardware layout, eg. the "no-dqs" property. You can take this on your shoulders if you want, but I would recommend not to, because this will require more patches and another round of review from DT maintainers which, I believe, we do not need at the moment. This DT property would be orthogonal and could very easily be added in a second step, keeping this series "small". Thanks, Miqu=C3=A8l