Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753010AbdHNWyQ (ORCPT ); Mon, 14 Aug 2017 18:54:16 -0400 Received: from mx0a-00010702.pphosted.com ([148.163.156.75]:46163 "EHLO mx0b-00010702.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752651AbdHNWyO (ORCPT ); Mon, 14 Aug 2017 18:54:14 -0400 From: Haris Okanovic To: , CC: , , , , , , , , , , , , , Subject: [PATCH] tpm_tis: fix stall after iowrite*()s Date: Mon, 14 Aug 2017 17:53:47 -0500 Message-ID: <20170814225347.30670-1-haris.okanovic@ni.com> X-Mailer: git-send-email 2.13.2 In-Reply-To: <20170804215651.29247-1-haris.okanovic@ni.com> References: <20170804215651.29247-1-haris.okanovic@ni.com> MIME-Version: 1.0 Content-Type: text/plain X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-08-14_20:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_policy_notspam policy=outbound_policy score=30 priorityscore=1501 malwarescore=0 suspectscore=2 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=30 reason=mlx scancount=1 engine=8.0.1-1706020000 definitions=main-1708140377 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2498 Lines: 70 ioread8() operations to TPM MMIO addresses can stall the cpu when immediately following a sequence of iowrite*()'s to the same region. For example, cyclitest measures ~400us latency spikes when a non-RT usermode application communicates with an SPI-based TPM chip (Intel Atom E3940 system, PREEMPT_RT_FULL kernel). The spikes are caused by a stalling ioread8() operation following a sequence of 30+ iowrite8()s to the same address. I believe this happens because the write sequence is buffered (in cpu or somewhere along the bus), and gets flushed on the first LOAD instruction (ioread*()) that follows. The enclosed change appears to fix this issue: read the TPM chip's access register (status code) after every iowrite*() operation to amortize the cost of flushing data to chip across multiple instructions. Signed-off-by: Haris Okanovic --- https://patchwork.kernel.org/patch/9882119/ https://github.com/harisokanovic/linux/tree/dev/hokanovi/tpm-latency-spike-fix --- drivers/char/tpm/tpm_tis.c | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) diff --git a/drivers/char/tpm/tpm_tis.c b/drivers/char/tpm/tpm_tis.c index c7e1384f1b08..3be2755d0514 100644 --- a/drivers/char/tpm/tpm_tis.c +++ b/drivers/char/tpm/tpm_tis.c @@ -52,6 +52,22 @@ static inline struct tpm_tis_tcg_phy *to_tpm_tis_tcg_phy(struct tpm_tis_data *da return container_of(data, struct tpm_tis_tcg_phy, priv); } +static inline void tpm_tis_iowrite8(u8 b, void __iomem *iobase, u32 addr) +{ + iowrite8(b, iobase + addr); +#ifdef CONFIG_PREEMPT_RT_FULL + ioread8(iobase + TPM_ACCESS(0)); +#endif +} + +static inline void tpm_tis_iowrite32(u32 b, void __iomem *iobase, u32 addr) +{ + iowrite32(b, iobase + addr); +#ifdef CONFIG_PREEMPT_RT_FULL + ioread8(iobase + TPM_ACCESS(0)); +#endif +} + static bool interrupts = true; module_param(interrupts, bool, 0444); MODULE_PARM_DESC(interrupts, "Enable interrupts"); @@ -105,7 +121,7 @@ static int tpm_tcg_write_bytes(struct tpm_tis_data *data, u32 addr, u16 len, struct tpm_tis_tcg_phy *phy = to_tpm_tis_tcg_phy(data); while (len--) - iowrite8(*value++, phy->iobase + addr); + tpm_tis_iowrite8(*value++, phy->iobase, addr); return 0; } @@ -129,7 +145,7 @@ static int tpm_tcg_write32(struct tpm_tis_data *data, u32 addr, u32 value) { struct tpm_tis_tcg_phy *phy = to_tpm_tis_tcg_phy(data); - iowrite32(value, phy->iobase + addr); + tpm_tis_iowrite32(value, phy->iobase, addr); return 0; } -- 2.13.2