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Thu, 23 Jul 2026 12:13:03 -0700 (PDT) From: Rosen Penev To: linux-ide@vger.kernel.org Cc: Damien Le Moal , Niklas Cassel , Rafal Prylowski , Jeff Garzik , linux-kernel@vger.kernel.org (open list) Subject: [PATCHv2] ata: pata_ep93xx: fix endianness bug in trailing byte transfer Date: Thu, 23 Jul 2026 12:13:02 -0700 Message-ID: <20260723191302.139580-1-rosenp@gmail.com> X-Mailer: git-send-email 2.55.0 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" ep93xx_pata_data_xfer() handles a trailing odd byte by reading/writing a full 16-bit word and extracting the first byte. The current code uses cpu_to_le16()/le16_to_cpu() wrapping, but then assigns through a u8 pointer (*pad), truncating the value. On the READ path, *pad =3D cpu_to_le16(...) truncates the u16 to u8. On little-endian this happens to give the right byte, but on big-endian cpu_to_le16() puts the valid byte in the upper 8 bits and truncation keeps the lower 8 bits (zeros), losing the data. On the WRITE path, le16_to_cpu(*pad) zero-extends pad[0] (u8) to u16 (0x00BB) and then on big-endian byte-swaps to 0xBB00. The hardware then receives 0x00 as the first byte instead of 0xBB. The readl()/writel() calls inside ep93xx_pata_read_data() and ep93xx_pata_write_data() already handle endianness correctly, so the trailing byte can just use the raw read/write value directly without the cpu_to_le16/le16_to_cpu wrappers. Remove the pad[] array and simplify. Fixes: 2fff27512600f9ad ("PATA host controller driver for ep93xx") Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-kbuild-all/202607231521.gvhnJpOG-lkp@int= el.com/ Assisted-by: Opencode:Big-Pickle Signed-off-by: Rosen Penev --- v2: add kernel bot fixes tags drivers/ata/pata_ep93xx.c | 11 ++--------- 1 file changed, 2 insertions(+), 9 deletions(-) diff --git a/drivers/ata/pata_ep93xx.c b/drivers/ata/pata_ep93xx.c index 339ee5e43e9f..558f9cf95e6e 100644 --- a/drivers/ata/pata_ep93xx.c +++ b/drivers/ata/pata_ep93xx.c @@ -499,19 +499,12 @@ static unsigned int ep93xx_pata_data_xfer(struct ata_= queued_cmd *qc, =20 /* Transfer trailing 1 byte, if any. */ if (unlikely(buflen & 0x01)) { - unsigned char pad[2] =3D { }; - buf +=3D buflen - 1; =20 if (rw =3D=3D READ) { - *pad =3D cpu_to_le16( - ep93xx_pata_read_data( - drv_data, IDECTRL_ADDR_DATA)); - *buf =3D pad[0]; + *buf =3D ep93xx_pata_read_data(drv_data, IDECTRL_ADDR_DATA); } else { - pad[0] =3D *buf; - ep93xx_pata_write_data(drv_data, le16_to_cpu(*pad), - IDECTRL_ADDR_DATA); + ep93xx_pata_write_data(drv_data, *buf, IDECTRL_ADDR_DATA); } words++; } --=20 2.55.0