From mboxrd@z Thu Jan 1 00:00:00 1970 From: Haris Okanovic Subject: [PATCH v2] tpm_tis: fix stall after iowrite*()s Date: Tue, 15 Aug 2017 15:13:08 -0500 Message-ID: <20170815201308.20024-1-haris.okanovic@ni.com> References: <20170804215651.29247-1-haris.okanovic@ni.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20170804215651.29247-1-haris.okanovic-acOepvfBmUk@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: tpmdd-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org To: linux-rt-users-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Cc: haris.okanovic-acOepvfBmUk@public.gmane.org, julia.cartwright-acOepvfBmUk@public.gmane.org, harisokn-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, jarkko.sakkinen-VuQAYsv1563Yd54FQh9/CA@public.gmane.org, eric.gardiner-acOepvfBmUk@public.gmane.org, jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org, jonathan.david-acOepvfBmUk@public.gmane.org, tpmdd-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, scott.hartman-acOepvfBmUk@public.gmane.org, chris.graf-acOepvfBmUk@public.gmane.org, gratian.crisan-acOepvfBmUk@public.gmane.org, brad.mouring-acOepvfBmUk@public.gmane.org List-Id: tpmdd-devel@lists.sourceforge.net 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 --- [PATCH v2] Add tpm_tis_flush() function with comment explaining the ioread8() after write, per Alexander. https://patchwork.kernel.org/patch/9882119/ https://github.com/harisokanovic/linux/tree/dev/hokanovi/tpm-latency-spike-fix-v2 --- drivers/char/tpm/tpm_tis.c | 29 +++++++++++++++++++++++++++-- 1 file changed, 27 insertions(+), 2 deletions(-) diff --git a/drivers/char/tpm/tpm_tis.c b/drivers/char/tpm/tpm_tis.c index c7e1384f1b08..3fdec13eba8d 100644 --- a/drivers/char/tpm/tpm_tis.c +++ b/drivers/char/tpm/tpm_tis.c @@ -52,6 +52,31 @@ 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); } +#ifdef CONFIG_PREEMPT_RT_FULL +/* + * Flushes previous write operations to chip so that a subsequent + * ioread*()s won't stall a cpu. + */ +static inline void tpm_tis_flush(void __iomem *iobase) +{ + ioread8(iobase + TPM_ACCESS(0)); +} +#else +#define tpm_tis_flush(iobase) do { } while (0) +#endif + +static inline void tpm_tis_iowrite8(u8 b, void __iomem *iobase, u32 addr) +{ + iowrite8(b, iobase + addr); + tpm_tis_flush(iobase); +} + +static inline void tpm_tis_iowrite32(u32 b, void __iomem *iobase, u32 addr) +{ + iowrite32(b, iobase + addr); + tpm_tis_flush(iobase); +} + static bool interrupts = true; module_param(interrupts, bool, 0444); MODULE_PARM_DESC(interrupts, "Enable interrupts"); @@ -105,7 +130,7 @@ 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 +154,7 @@ 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 ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot