From mboxrd@z Thu Jan 1 00:00:00 1970 From: Shinya Kuribayashi Subject: [PATCH 3/5] i2c: i2c-sh_mobile: fix ICCH to avoid violation of the tHD;STA timing spec Date: Wed, 24 Oct 2012 19:57:51 +0900 Message-ID: <5087C9AF.409@renesas.com> References: <5087C93F.6080601@renesas.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-reply-to: <5087C93F.6080601@renesas.com> Sender: linux-sh-owner@vger.kernel.org To: w.sang@pengutronix.de, ben-linux@fluff.org, magnus.damm@gmail.com Cc: linux-i2c@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-sh@vger.kernel.org List-Id: linux-i2c@vger.kernel.org The optimized ICCH/ICCL values in the previous commit afterward turned out to violate tHD;STA timing spec. We had to take into account the fall time of SDA signal (tf) at START condition. Fix it accordingly. With this change, sh_mobile_i2c_icch() is virtually identical to sh_mobile_i2c_iccl(), but they're providing good descriptions of SH-/R-Mobile I2C hardware spec, and I'd leave them as separated. Signed-off-by: Shinya Kuribayashi --- drivers/i2c/busses/i2c-sh_mobile.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/drivers/i2c/busses/i2c-sh_mobile.c b/drivers/i2c/busses/i2c-sh_mobile.c index 1ad80c9..4dc0cc3 100644 --- a/drivers/i2c/busses/i2c-sh_mobile.c +++ b/drivers/i2c/busses/i2c-sh_mobile.c @@ -203,18 +203,23 @@ static u32 sh_mobile_i2c_iccl(unsigned long count_khz, u32 tLOW, u32 tf, int off return (((count_khz * (tLOW + tf)) + 5000) / 10000) + offset; } -static u32 sh_mobile_i2c_icch(unsigned long count_khz, u32 tHIGH, int offset) +static u32 sh_mobile_i2c_icch(unsigned long count_khz, u32 tHIGH, u32 tf, int offset) { /* * Conditional expression: - * ICCH >= COUNT_CLK * tHIGH + * ICCH >= COUNT_CLK * (tHIGH + tf) * * SH-Mobile IIC hardware is aware of SCL transition period 'tr', * and can ignore it. SH-Mobile IIC controller starts counting * the HIGH period of the SCL signal (tHIGH) after the SCL input * voltage increases at VIH. + * + * Afterward it turned out calculating ICCH using only tHIGH spec + * will result in violation of the tHD;STA timing spec. We need + * to take into account the fall time of SDA signal (tf) at START + * condition, in order to meet both tHIGH and tHD;STA specs. */ - return ((count_khz * tHIGH) + 5000) / 10000 + offset; + return (((count_khz * (tHIGH + tf)) + 5000) / 10000) + offset; } static void sh_mobile_i2c_init(struct sh_mobile_i2c_data *pd) @@ -250,7 +255,7 @@ static void sh_mobile_i2c_init(struct sh_mobile_i2c_data *pd) else pd->icic &= ~ICIC_ICCLB8; - pd->icch = sh_mobile_i2c_icch(i2c_clk_khz, tHIGH, offset); + pd->icch = sh_mobile_i2c_icch(i2c_clk_khz, tHIGH, tf, offset); /* one more bit of ICCH in ICIC */ if ((pd->icch > 0xff) && (pd->flags & IIC_FLAG_HAS_ICIC67)) pd->icic |= ICIC_ICCHB8; -- 1.7.12.4