From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 67871407573; Wed, 1 Apr 2026 11:00:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775041225; cv=none; b=AS+S2SQzjgZv7zMG/xpLpsJnP8NMfSys6qQ+1kc+1fmNqyyAcCLfoh5pPEOXQ8uJXcmYT78/SkZsoUrbZ5Rfjx90KbbzMxLjGYYTeAwWJtWjQAHOGQ1I8zzwoEhPOU1RJKrvJiqY0Y2FF4NgscYIWHF6uoLL/azCKK57KvZjy3I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775041225; c=relaxed/simple; bh=P4gPDzIC37mQ2XU2ES1ReyzNW1zgfb4XNdW83riZvtY=; h=Mime-Version:Content-Type:Date:Message-Id:Subject:Cc:From:To: References:In-Reply-To; b=ZgTKHqFQTOrp4Kt7BfkOrMlNUgwMG/GYCgaoinxovAWDEwjxrsqpMOyW43oc1YlHI6+hZfM1obtKxJVvQKWTViapYLUa7p7B3RyD8w1GOXFvAwjmomePEMla6ppm2+JXU8/0gthzo1XbBOVVGSs6FLldpfahFbNejo7/MboYSNE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=sFSPKFYw; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="sFSPKFYw" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A1F7EC4CEF7; Wed, 1 Apr 2026 11:00:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775041225; bh=P4gPDzIC37mQ2XU2ES1ReyzNW1zgfb4XNdW83riZvtY=; h=Date:Subject:Cc:From:To:References:In-Reply-To:From; b=sFSPKFYweFFOdfbH0OagWFKdwhTq+1MKRsDYRdV0xhvI13BSdEYfJPfUUliaIsPZ8 59delv7rophLlaAEkA816DG+xemnbsLMn18Z6kK1y4E1ZuyYuvEiMYmsbG4+rvLY3I Qg0dOE9Aeo4I0uV48WTnU4mWriwqWLJfSDHwy6X+fp3uaudWzUyNUbrd3BFgqVMo83 tMI5nivsa18n4OrbifXTgH/cIcjG+hjs8npXnLpiNmTcbPCtrDpksT6Q7eFhIbhR0B +2LuH1JNsqXCPyTqkH3RAMie5qpNbRxJA/H/Fk6ORUkatElASRqgw/y/0ofC3NGIDj UyiGqB+8ucCjg== Precedence: bulk X-Mailing-List: linux-spi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: multipart/signed; boundary=20ef4b1937c524c4b5e1cf3c92e15c2d5ceb7be4f72bca70e5220b66a6c0; micalg=pgp-sha384; protocol="application/pgp-signature" Date: Wed, 01 Apr 2026 13:00:20 +0200 Message-Id: Subject: Re: [PATCH RFC 6/7] spi: spi-mem: Call spi_set_rx_sampling_point() for each op Cc: "Frieder Schrempf" , "Mark Brown" , "Richard Weinberger" , "Vignesh Raghavendra" , "Han Xu" , "Eberhard Stoll" , "Tudor Ambarus" , "Pratyush Yadav" , , , , , "Santhosh Kumar K" From: "Michael Walle" To: "Miquel Raynal" , "Frieder Schrempf" X-Mailer: aerc 0.20.0 References: <20260303-fsl-qspi-rx-sampling-delay-v1-0-9326bbc492d6@kontron.de> <20260303-fsl-qspi-rx-sampling-delay-v1-6-9326bbc492d6@kontron.de> <87wlzlnioh.fsf@bootlin.com> <87ecl09wtv.fsf@bootlin.com> <633fee13-a397-410f-a595-db95e04b8110@kontron.de> <87ldf881gr.fsf@bootlin.com> <874ilv84j8.fsf@bootlin.com> In-Reply-To: <874ilv84j8.fsf@bootlin.com> --20ef4b1937c524c4b5e1cf3c92e15c2d5ceb7be4f72bca70e5220b66a6c0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 On Wed Apr 1, 2026 at 10:32 AM CEST, Miquel Raynal wrote: >> Let's say for a worst case scenario a chip has an RX delay of 20ns (the >> highest I've seen in datasheets so far is 8ns). In that case the maximum >> clock we could safely use for reading the ID would be 1/(2*20e-9) =3D >> 25MHz. Do you think it really makes much of a difference if we read the >> ID (only a handful of bytes) at 25MHz or full speed (e. g. 104 MHz)? I >> mean this should be fast enough either way, no? But maybe I'm misjudging >> this. > > I am honestly not a big fan of the global penalty, but I am not totally > opposed either, especially since you just said you only observed 8ns > delays at most. This is 62.5MHz, which is already above what most > designs use, so the penalty would be minimal. What about taking this > approach and see if that fixes most of our use cases? What are the actual numbers we are talking about here? I mean, at least for SPI NOR, we only read the ID *once*. And it takes about 56 bits (command + id length of 6). That is about 2us at 25MHz. I'd guess the setup and the software handling takes far longer than that. -michael --20ef4b1937c524c4b5e1cf3c92e15c2d5ceb7be4f72bca70e5220b66a6c0 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iKgEABMJADAWIQTIVZIcOo5wfU/AngkSJzzuPgIf+AUCacz6xRIcbXdhbGxlQGtl cm5lbC5vcmcACgkQEic87j4CH/jivwF7BfdJ2oJO2K3l5ud626MmhRiz2MLQbewR E5u5gITBAhN2jHdEai/ryzBXc5JvEBklAYCLd3qRamZ8b67NsNkXMP4lXC5UL7VN gh53mq8O5Msc590EhY5l3GZxv8zwbYJGhFU= =FqVe -----END PGP SIGNATURE----- --20ef4b1937c524c4b5e1cf3c92e15c2d5ceb7be4f72bca70e5220b66a6c0--