From mboxrd@z Thu Jan 1 00:00:00 1970 From: Srinivas Kandagatla Subject: Re: [PATCH v1 06/11] mmc: mmci: Qcomm: Add 3 clock cycle delay after register write Date: Tue, 13 May 2014 10:14:13 +0100 Message-ID: <5371E265.4020603@linaro.org> References: <1398759492-12970-1-git-send-email-srinivas.kandagatla@linaro.org> <1398759614-13217-1-git-send-email-srinivas.kandagatla@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Linus Walleij Cc: Russell King , "linux-mmc@vger.kernel.org" , Chris Ball , Ulf Hansson , "linux-kernel@vger.kernel.org" , agross@quicinc.com, "linux-arm-msm@vger.kernel.org" List-Id: linux-arm-msm@vger.kernel.org Thanks Linus W for reviewing the patches. On 13/05/14 08:29, Linus Walleij wrote: > On Tue, Apr 29, 2014 at 10:20 AM, wrote: > >> From: Srinivas Kandagatla >> >> Most of the Qcomm SD card controller registers must be updated to the MCLK >> domain so subsequent writes to registers will be ignored until 3 clock cycles >> have passed. >> >> This patch adds a 3 clock cycle delay required after writing to controller >> registers on Qualcomm SOCs. Without this delay all the register writes are not >> successfull, resulting in not detecting cards. >> >> Signed-off-by: Srinivas Kandagatla > > Sounds like someone decided to clock the internal state machine > in the MMCI using MCLK instead of PCLK :-( > > A bit nasty if this ends up in the fastpath (irq) though. Which it > invariably does, right? yes, Its going to for Qcom SOC. > >> + /* >> + * On QCom SD card controller, registers must be updated to the >> + * MCLK domain so subsequent writes to this register will be ignored >> + * for 3 clk cycles. >> + */ >> + if (host->hw_designer == AMBA_VENDOR_QCOM) >> + udelay(1 + ((3 * USEC_PER_SEC)/host->mclk)); > > Add a new field in vendor data instead, and use DIV_ROUND_UP(): > yes, that makes sense.. > static struct variant_data variant_qcom = { > .mclk_delayed_writes = true, > (...) > > if (host->vendor->mclk_delayed_writes) > udelay(DIV_ROUND_UP((3 * USEC_PER_SEC), host->mclk)); > > You get the idea. > Got it. > Yours, > Linus Walleij >