>> On Aug 21, 2015 3:10 PM, "Yaniv Gardi" <ygardi@xxxxxxxxxxxxxx> 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 <ygardi@xxxxxxxxxxxxxx> >>> >>> --- >>> 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@xxxxxxxxxxxxxxx >> 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@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
