From nobody Wed Feb 5 20:46:30 2025 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 06A7E24A7F1 for ; Wed, 15 Jan 2025 13:42:21 +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=1736948542; cv=none; b=QQPGZxH0b6/cDbJUzqGCkbm1TXSLX9h86EVgAEwygbabmMV/8FZrO6g/tfiAg2nuB6Tszk4GOBnIvGy6zBBl1p1JAziCWZOyHtrHpSntdnKgKdWcwjrZhcwBvSR4V14FRloXGl3IpwLf+NLonML8ljyUHS4/ZmcwpVFiI1bLrAY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736948542; c=relaxed/simple; bh=T92rSxsCbibHVE1GcYfXql/KUtyqXXsf7RSMuXZZBzw=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=KAegoPw2TuF7ZcgCowxq9GpdpAMX9YwGHEHQBlYBprJFwqmQsjxIPlj1t86+IcLNj/cfV1woV+12wLyknDmB21Ij0QppFthJzoZcCDagAWoG6DtobDRpvL7gP+FHnx0tymM9eUn6WiQEreZ1Ym/LByr4EMwc0NVeYdtyF6ooOo0= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MNiNa8PS; 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="MNiNa8PS" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AC458C4CEDF; Wed, 15 Jan 2025 13:42:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1736948541; bh=T92rSxsCbibHVE1GcYfXql/KUtyqXXsf7RSMuXZZBzw=; h=From:To:Cc:Subject:Date:From; b=MNiNa8PStD5CQJFcaCV+mqG09tEWjMDHZd7VEwp7itG2WL1W77aGTQUpnx1cl7/z6 pWo0wkYQM+KK6szy/dKuyUSFLoaqR80DrCbkKljrIQWlJpchNVqdsKSZqb5UJ1uzAu E9PwR71m5AITkjyaLWeK/fI1wa+KOREBqjtFtaqNQ/GjQn0z5b0yRRWI6ByEZeCH+Z eJ07ker5b924/Zgqvp+RL2adzz89YiKNzIchkD3m4C/Slm0OEB9kWRd3KeJ7KdoN67 oiyrEdIZFzJQnNamrLJ0RLOpIIEUQ8di2Er86euuXu9qgdnX/gcmQh2ZIp9+yZwDS9 mefl3Gukxbu+g== From: Pratyush Yadav To: Tudor Ambarus , Pratyush Yadav , Michael Walle , Miquel Raynal , Richard Weinberger , Vignesh Raghavendra , Cheng Ming Lin , Alexander Stein Cc: linux-kernel@vger.kernel.org, linux-mtd@lists.infradead.org, alvinzhou@mxic.com.tw, leoyu@mxic.com.tw, Cheng Ming Lin Subject: [PATCH v2] Revert "mtd: spi-nor: core: replace dummy buswidth from addr to data" Date: Wed, 15 Jan 2025 13:41:56 +0000 Message-ID: <20250115134158.19908-1-pratyush@kernel.org> X-Mailer: git-send-email 2.48.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" This reverts commit 98d1fb94ce75f39febd456d6d3cbbe58b6678795. The commit uses data nbits instead of addr nbits for dummy phase. This causes a regression for all boards where spi-tx-bus-width is smaller than spi-rx-bus-width. It is a common pattern for boards to have spi-tx-bus-width =3D=3D 1 and spi-rx-bus-width > 1. The regression causes all reads with a dummy phase to become unavailable for such boards, leading to a usually slower 0-dummy-cycle read being selected. Most controllers' supports_op hooks call spi_mem_default_supports_op(). In spi_mem_default_supports_op(), spi_mem_check_buswidth() is called to check if the buswidths for the op can actually be supported by the board's wiring. This wiring information comes from (among other things) the spi-{tx,rx}-bus-width DT properties. Based on these properties, SPI_TX_* or SPI_RX_* flags are set by of_spi_parse_dt(). spi_mem_check_buswidth() then uses these flags to make the decision whether an op can be supported by the board's wiring (in a way, indirectly checking against spi-{rx,tx}-bus-width). Now the tricky bit here is that spi_mem_check_buswidth() does: if (op->dummy.nbytes && spi_check_buswidth_req(mem, op->dummy.buswidth, true)) return false; The true argument to spi_check_buswidth_req() means the op is treated as a TX op. For a board that has say 1-bit TX and 4-bit RX, a 4-bit dummy TX is considered as unsupported, and the op gets rejected. The commit being reverted uses the data buswidth for dummy buswidth. So for reads, the RX buswidth gets used for the dummy phase, uncovering this issue. In reality, a dummy phase is neither RX nor TX. As the name suggests, these are just dummy cycles that send or receive no data, and thus don't really need to have any buswidth at all. Ideally, dummy phases should not be checked against the board's wiring capabilities at all, and should only be sanity-checked for having a sane buswidth value. Since we are now at rc7 and such a change might introduce many unexpected bugs, revert the commit for now. It can be sent out later along with the spi_mem_check_buswidth() fix. Fixes: 98d1fb94ce75 ("mtd: spi-nor: core: replace dummy buswidth from addr = to data") Reported-by: Alexander Stein Closes: https://lore.kernel.org/linux-mtd/3342163.44csPzL39Z@steina-w/ Tested-by: Alexander Stein Reviewed-by: Tudor Ambarus Signed-off-by: Pratyush Yadav --- Changes in v2: - Add R-by from Tudor and T-by from Alexander. - Make "This reverts commit..." its own paragraph - Add fixes tag. drivers/mtd/spi-nor/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c index 66949d9f0cc5..b6f374ded390 100644 --- a/drivers/mtd/spi-nor/core.c +++ b/drivers/mtd/spi-nor/core.c @@ -89,7 +89,7 @@ void spi_nor_spimem_setup_op(const struct spi_nor *nor, op->addr.buswidth =3D spi_nor_get_protocol_addr_nbits(proto); if (op->dummy.nbytes) - op->dummy.buswidth =3D spi_nor_get_protocol_data_nbits(proto); + op->dummy.buswidth =3D spi_nor_get_protocol_addr_nbits(proto); if (op->data.nbytes) op->data.buswidth =3D spi_nor_get_protocol_data_nbits(proto); -- 2.40.1