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Tue, 11 Aug 2026 02:09:28 -0700 (PDT) Message-ID: Date: Tue, 11 Aug 2026 10:09:27 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 6.12.y] spi: spi-fsl-dspi: Avoid setup_accel logic for DMA transfers To: Mehmet Fide , stable@vger.kernel.org, Larisa Grigore , Vladimir Oltean Cc: Greg Kroah-Hartman , Sasha Levin , Mark Brown , linux-spi@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260810141437.2805389-1-mehmet.fide@gmail.com> <20260811084018.3566861-1-mehmet.fide@gmail.com> Content-Language: en-US From: James Clark In-Reply-To: <20260811084018.3566861-1-mehmet.fide@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 11/08/2026 09:40, Mehmet Fide wrote: > Some measurements on the hardware, in case they help decide this one. > > I ran the transfers that fail on 6.12 against 6.18.44, which carries > cac7e5054115, on the same board (Colibri VF50, vf610, DSPI in DMA mode) with > MOSI and MISO shorted at the connector, using spidev_test: > > 3, 5, 7, 9, 11 and 13 byte transfers: every byte comes back, in order. > Even lengths and a single byte: fine as well. > SPI_LSB_FIRST at 2, 3, 5, 8 and 13 bytes: bytes come back unchanged. > > Without the commit, the same odd length transfers lose the tail of the buffer, > because the accel path packs into 16 bit frames and computes the word count as > len / 2, and SPI_LSB_FIRST comes back byte swapped, because the accel helpers > byte swap through cpu_to_be16() on top of the hardware LSBFE bit. That is what > we have been carrying a local equivalent for. > > So the commit is what makes those transfers correct on this hardware, not just > a saving of pointless repacking. > > Thanks, > Mehmet It's possible that this was originally done as a fix but I interpreted it as a refactor. As part of upstreaming this I broke down and added commit messages to changes from NXPs board support branch. It does make sense that this change was added after seeing the bug, rather than just a clean up. But it could also be a coincidence. James