From patchwork Wed Aug 3 14:58:57 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Robin Murphy X-Patchwork-Id: 12935601 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3264EC3F6B0 for ; Wed, 3 Aug 2022 14:59:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234349AbiHCO7E (ORCPT ); Wed, 3 Aug 2022 10:59:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38950 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233526AbiHCO7E (ORCPT ); Wed, 3 Aug 2022 10:59:04 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 7552613E91; Wed, 3 Aug 2022 07:59:02 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E7FD811FB; Wed, 3 Aug 2022 07:59:02 -0700 (PDT) Received: from e121345-lin.cambridge.arm.com (e121345-lin.cambridge.arm.com [10.1.196.40]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id A98DB3F70D; Wed, 3 Aug 2022 07:59:01 -0700 (PDT) From: Robin Murphy To: broonie@kernel.org Cc: linux-spi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] spi: bitbang: Fix lsb-first Rx Date: Wed, 3 Aug 2022 15:58:57 +0100 Message-Id: <28324d8622da80461cce35a82859b003d6f6c4b0.1659538737.git.robin.murphy@arm.com> X-Mailer: git-send-email 2.36.1.dirty MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-spi@vger.kernel.org Shifting the recieved bit by "bits" inserts it at the top of the *currently remaining* Tx data, so we end up accumulating the whole transfer into bit 0 of the output word. Oops. For the algorithm to work as intended, we need to remember where the top of the *original* word was, and shift Rx to there. Fixes: 1847e3046c52 ("spi: gpio: Implement LSB First bitbang support") Signed-off-by: Robin Murphy --- drivers/spi/spi-bitbang-txrx.h | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/spi/spi-bitbang-txrx.h b/drivers/spi/spi-bitbang-txrx.h index 267342dfa738..2dcbe166df63 100644 --- a/drivers/spi/spi-bitbang-txrx.h +++ b/drivers/spi/spi-bitbang-txrx.h @@ -116,6 +116,7 @@ bitbang_txrx_le_cpha0(struct spi_device *spi, { /* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */ + u8 rxbit = bits - 1; u32 oldbit = !(word & 1); /* clock starts at inactive polarity */ for (; likely(bits); bits--) { @@ -135,7 +136,7 @@ bitbang_txrx_le_cpha0(struct spi_device *spi, /* sample LSB (from slave) on leading edge */ word >>= 1; if ((flags & SPI_MASTER_NO_RX) == 0) - word |= getmiso(spi) << (bits - 1); + word |= getmiso(spi) << rxbit; setsck(spi, cpol); } return word; @@ -148,6 +149,7 @@ bitbang_txrx_le_cpha1(struct spi_device *spi, { /* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */ + u8 rxbit = bits - 1; u32 oldbit = !(word & 1); /* clock starts at inactive polarity */ for (; likely(bits); bits--) { @@ -168,7 +170,7 @@ bitbang_txrx_le_cpha1(struct spi_device *spi, /* sample LSB (from slave) on trailing edge */ word >>= 1; if ((flags & SPI_MASTER_NO_RX) == 0) - word |= getmiso(spi) << (bits - 1); + word |= getmiso(spi) << rxbit; } return word; }