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[61.216.91.114]) by smtp.gmail.com with ESMTPSA id v12sm69958469pgg.41.2018.11.25.18.30.36 (version=TLS1_2 cipher=AES128-SHA bits=128/128); Sun, 25 Nov 2018 18:30:39 -0800 (PST) Date: Mon, 26 Nov 2018 10:30:23 +0800 From: Shawn Guo To: Kishon Vijay Abraham I Cc: Rob Herring , Sriharsha Allenki , Anu Ramanathan , Bjorn Andersson , Vinod Koul , linux-arm-msm@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 2/2] phy: qualcomm: Add Synopsys High-Speed USB PHY driver Message-ID: <20181126023021.GC20417@dragon> References: <20181119110812.15825-1-shawn.guo@linaro.org> <20181119110812.15825-3-shawn.guo@linaro.org> <52433bdc-bc05-2ca0-0822-c9fb702b3231@ti.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <52433bdc-bc05-2ca0-0822-c9fb702b3231@ti.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 23, 2018 at 03:25:33PM +0530, Kishon Vijay Abraham I wrote: > > +static int qcom_snps_hsphy_por_reset(struct hsphy_priv *priv) > > +{ > > + int ret; > > + > > + ret = reset_control_assert(priv->por_reset); > > + if (ret) > > + return ret; > > + > > + /* > > + * The Femto PHY is POR reset in the following scenarios. > > + * > > + * 1. After overriding the parameter registers. > > + * 2. Low power mode exit from PHY retention. > > + * > > + * Ensure that SIDDQ is cleared before bringing the PHY > > + * out of reset. > > + */ > > + qcom_snps_hsphy_exit_retention(priv); > > + > > + /* > > + * As per databook, 10 usec delay is required between > > + * PHY POR assert and de-assert. > > + */ > > + usleep_range(10, 20); > > + ret = reset_control_deassert(priv->por_reset); > > + if (ret) > > + return ret; > > + > > + /* > > + * As per databook, it takes 75 usec for PHY to stabilize > > + * after the reset. > > + */ > > + usleep_range(80, 100); > > + > > + /* Ensure that RESET operation is completed. */ > > + mb(); > > How will you ensure the reset operation is complete with a memory barrier? mb > usage here looks incorrect to me. I agree with you, Kishon. I think memory barrier only ensures the register write happens rather than that RESET operation completes. Since the IO accessors already handle memory barrier, I will just drop the mb() from here and function qcom_snps_hsphy_init_sequence() as well. @Sriharsha, let us know if you have a story or reason for these memory barriers. Shawn