Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753917AbbH0M2a (ORCPT ); Thu, 27 Aug 2015 08:28:30 -0400 Received: from smtp.codeaurora.org ([198.145.29.96]:37362 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753871AbbH0M21 (ORCPT ); Thu, 27 Aug 2015 08:28:27 -0400 Message-ID: In-Reply-To: <1408ea96f7b8f33aef73e0f84abd8792.squirrel@www.codeaurora.org> References: <1440194989-28835-1-git-send-email-ygardi@codeaurora.org> <1440194989-28835-15-git-send-email-ygardi@codeaurora.org> <1408ea96f7b8f33aef73e0f84abd8792.squirrel@www.codeaurora.org> Date: Thu, 27 Aug 2015 12:28:25 -0000 Subject: Re: [PATCH v1 14/15] scsi: ufs: commit descriptors before setting the doorbell From: ygardi@codeaurora.org To: ygardi@codeaurora.org Cc: "Rob Herring" , "Yaniv Gardi" , "linux-arm-msm" , linux-scsi@vger.kernel.org, "Dolev Raviv" , "Gilad Broner" , linux-scsi-owner@vger.kernel.org, "Jej B" , "Santosh Y" , "Subhash Jadavani" , hch@infradead.org, "Paul Bolle" , "James E.J. Bottomley" , "Vinayak Holikatti" , "linux-kernel@vger.kernel.org" User-Agent: SquirrelMail/1.4.22-4.el6 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Priority: 3 (Normal) Importance: Normal Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3788 Lines: 107 >> On Aug 21, 2015 3:10 PM, "Yaniv Gardi" wrote: >>> >>> Add a write memory barrier to make sure descriptors prepared are >>> actually >>> written to memory before ringing the doorbell. We have also added the >>> write memory barrier after ringing the doorbell register so that >>> controller sees the new request immediately. >>> >>> Signed-off-by: Yaniv Gardi >>> >>> --- >>> drivers/scsi/ufs/ufshcd.c | 6 ++++++ >>> 1 file changed, 6 insertions(+) >>> >>> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c >>> index fef0660..876148b 100644 >>> --- a/drivers/scsi/ufs/ufshcd.c >>> +++ b/drivers/scsi/ufs/ufshcd.c >>> @@ -833,6 +833,8 @@ void ufshcd_send_command(struct ufs_hba *hba, >>> unsigned int task_tag) >>> ufshcd_clk_scaling_start_busy(hba); >>> __set_bit(task_tag, &hba->outstanding_reqs); >>> ufshcd_writel(hba, 1 << task_tag, >>> REG_UTP_TRANSFER_REQ_DOOR_BELL); >>> + /* Make sure that doorbell is committed immediately */ >>> + wmb(); >> >> Is this really necessary? Is there a measurable difference? > > I'm not sure if there is a measurable difference, but as the Door-Bell > register is the one that actually responsible for the HW execution of the > requests, anyhow, it's recommended to its value will be written > instantly to the memory. > > Also, as the Interrupt context reads this register, and compare it to the > SW mirroring value (hba->outstanding_reqs) in order to realize what > requests are already completed, it's important to get the correct value > by reading this register, otherwise we might realize a request completion > while it was never even submitted. > >> >>> } >>> >>> /** >>> @@ -1418,6 +1420,8 @@ static int ufshcd_queuecommand(struct Scsi_Host >>> *host, struct scsi_cmnd *cmd) >>> goto out; >>> } >>> >>> + /* Make sure descriptors are ready before ringing the doorbell >>> */ >>> + wmb(); >> >> The writel for the doorbell will do a barrier first. (I didn't check >> what exactly ufshcd_writel does, but that is why I don't like these >> private access wrappers.) the barrier here is important and a must. before it we prepare descriptors. after it we write to DOOR-BELL. (and after the DOOR-BELL we have another one.) if we remove it, we might get the DOOR-BELL written, before the descriptors written. >> >>> /* issue command to the controller */ >>> spin_lock_irqsave(hba->host->host_lock, flags); >>> ufshcd_send_command(hba, tag); >>> @@ -1627,6 +1631,8 @@ static int ufshcd_exec_dev_cmd(struct ufs_hba >>> *hba, >>> >>> hba->dev_cmd.complete = &wait; >>> >>> + /* Make sure descriptors are ready before ringing the doorbell >>> */ >>> + wmb(); >>> spin_lock_irqsave(hba->host->host_lock, flags); >>> ufshcd_send_command(hba, tag); >>> spin_unlock_irqrestore(hba->host->host_lock, flags); >>> -- >>> 1.8.5.2 >>> >>> -- >>> QUALCOMM ISRAEL, on behalf of Qualcomm Innovation Center, Inc. is a >>> member of Code Aurora Forum, hosted by The Linux Foundation >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-scsi" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-scsi" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/