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arc=none smtp.client-ip=217.70.183.198 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=bootlin.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=bootlin.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=bootlin.com header.i=@bootlin.com header.b="hU6IkXoa" Received: by mail.gandi.net (Postfix) with ESMTPSA id 82280C0007; Tue, 24 Dec 2024 09:38:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=gm1; t=1735033082; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=gBPPOxtHffFdeWaNXscLfKp/7O7VkfykoygWXPPAjsg=; b=hU6IkXoaqfaaCeRa5aRTsich4mHwfabEBJ7s0XQFIKyaaLODFmp9F8pGEfdVOijjhHsSNF HBuPIaKEgcumcS23+bZ+pq3O0ETBZIRn0lSB8GrnzIn7d1S9mFmS3zPrxggFW4QfkDQXJ+ nlK5Zn+IWyst59ZwvqtSCB7CwsxBFbe39NpLbDp5L//EfDUunAAuPayw3Z9EPk3CBR+lOQ wXRrYB36+++R/OQgKMzkVdVosOhlKq2WuWfz5iUHuqckvvH1lUZqoApbJCEscqhJR2OXok lBwBhbcWPeMxlOOQDkm+ZYX4ReJW54KtdCpjxSMGGVEt1akUVXIxQxRwGH8sLg== From: Miquel Raynal To: Tudor Ambarus Cc: Richard Weinberger , Vignesh Raghavendra , Pratyush Yadav , Michael Walle , linux-mtd@lists.infradead.org, Mark Brown , linux-spi@vger.kernel.org, Steam Lin , Thomas Petazzoni , Sanjay R Mehta , Han Xu , Conor Dooley , Daire McNamara , Matthias Brugger , AngeloGioacchino Del Regno , Haibo Chen , Yogesh Gaur , Heiko Stuebner , Michal Simek Subject: Re: [PATCH 24/24] mtd: spinand: winbond: Add support for DTR operations In-Reply-To: <87o712uunf.fsf@bootlin.com> (Miquel Raynal's message of "Mon, 23 Dec 2024 19:22:12 +0100") References: <20241025161501.485684-1-miquel.raynal@bootlin.com> <20241025161501.485684-25-miquel.raynal@bootlin.com> <6029a01f-dc4d-4a35-ad21-fd17e3fed9fc@linaro.org> <87o712uunf.fsf@bootlin.com> User-Agent: mu4e 1.12.7; emacs 29.4 Date: Tue, 24 Dec 2024 10:38:00 +0100 Message-ID: <87ttato1zb.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-GND-Sasl: miquel.raynal@bootlin.com Hello Tudor, On 23/12/2024 at 19:22:12 +01, Miquel Raynal wr= ote: > Hello Tudor, > > On 11/11/2024 at 14:40:59 GMT, Tudor Ambarus w= rote: > >> On 10/25/24 5:15 PM, Miquel Raynal wrote: >>> W25N01JW and W25N02JW support many DTR read modes in single, dual and >>> quad configurations. >>>=20 >>> DTR modes however cannot be used at 166MHz, as the bus frequency in >>> this case must be lowered to 80MHz. >> >> ha, what's the benefit then? Aren't we better of with non dtr modes >> then? 80 MHz * 2 < 166 MHz? > > This is actually a good question, and you are right DDR in this case > does not bring better throughputs, it can even make it a little bit > slower. I think however we should expect some gains at the PCB design > step, which may be way simpler as routing 8 166MHz lines might > apparently be challenging. It is common to have PCB limitations on the > frequency, so enabling DDR can be a great way to keep signal integrity > while definitely improving the performances. However, you're right, I > should probably move these definitions lower in the table to make sure > we run at 166MHz if that's possible. Actually this is probably not a good solution. This stable is parsed once from top to bottom. The elements order decide whether we'll use a variant or another, not by deciding which one is the fastest, but by taking the first one that fits. But with DTR operations it no longer works so well. If I list items like that: SPINAND_PAGE_READ_FROM_CACHE_QUADIO_DTR_OP(0, 8, NULL, 0, 80 * HZ_PER_MHZ), SPINAND_PAGE_READ_FROM_CACHE_QUADIO_OP(0, 2, NULL, 0 /* 166 MHz */), It is likely that I will not run at the fastest possible throughput, ie about 160MHz instead of 166MHz. But if I do the reverse: SPINAND_PAGE_READ_FROM_CACHE_QUADIO_OP(0, 2, NULL, 0 /* 166 MHz */), SPINAND_PAGE_READ_FROM_CACHE_QUADIO_DTR_OP(0, 8, NULL, 0, 80 * HZ_PER_MHZ), I will only run at the fastest throughput if the PCB lines are so well designed that they can support 166MHz. If they only support 150MHz (or anything lower) it would have been better to pick the DTR op. My conclusion is: the current logic needs to be improved, so I'm drafting a slightly more complex variant picker which will evaluate the theoretical length of an op based on the speed, parallel lines, DTR capability, etc. This way the order in this table will no longer matter. I will soon respin a series because I've enhanced a lot of things inside. Cheers, Miqu=C3=A8l