2021-09-07 06:29:36

by Pawel Laszczak

Subject: [PATCH] usb: cdns3: fix race condition before setting doorbell

From: Pawel Laszczak <[email protected]>

For DEV_VER_V3 version there exist race condition between clearing
ep_sts.EP_STS_TRBERR and setting ep_cmd.EP_CMD_DRDY bit.
Setting EP_CMD_DRDY will be ignored by controller when
EP_STS_TRBERR is set. So, between these two instructions we have
a small time gap in which the EP_STSS_TRBERR can be set. In such case
the transfer will not start after setting doorbell.

Fixes: 7733f6c32e36 ("usb: cdns3: Add Cadence USB3 DRD Driver")
cc: <[email protected]> # 5.12.x
Signed-off-by: Pawel Laszczak <[email protected]>
---
drivers/usb/cdns3/cdns3-gadget.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)

diff --git a/drivers/usb/cdns3/cdns3-gadget.c b/drivers/usb/cdns3/cdns3-gadget.c
index 80aaab159e58..e9769fab21ea 100644
--- a/drivers/usb/cdns3/cdns3-gadget.c
+++ b/drivers/usb/cdns3/cdns3-gadget.c
@@ -1100,6 +1100,19 @@ static int cdns3_ep_run_stream_transfer(struct cdns3_endpoint *priv_ep,
return 0;
}

+static void cdns3_rearm_drdy_if_needed(struct cdns3_endpoint *priv_ep)
+{
+ struct cdns3_device *priv_dev = priv_ep->cdns3_dev;
+
+ if (priv_dev->dev_ver < DEV_VER_V3)
+ return;
+
+ if (readl(&priv_dev->regs->ep_sts) & EP_STS_TRBERR) {
+ writel(EP_STS_TRBERR, &priv_dev->regs->ep_sts);
+ writel(EP_CMD_DRDY, &priv_dev->regs->ep_cmd);
+ }
+}
+
/**
* cdns3_ep_run_transfer - start transfer on no-default endpoint hardware
* @priv_ep: endpoint object
@@ -1351,6 +1364,7 @@ static int cdns3_ep_run_transfer(struct cdns3_endpoint *priv_ep,
/*clearing TRBERR and EP_STS_DESCMIS before seting DRDY*/
writel(EP_STS_TRBERR | EP_STS_DESCMIS, &priv_dev->regs->ep_sts);
writel(EP_CMD_DRDY, &priv_dev->regs->ep_cmd);
+ cdns3_rearm_drdy_if_needed(priv_ep);
trace_cdns3_doorbell_epx(priv_ep->name,
readl(&priv_dev->regs->ep_traddr));
}
--
2.25.1

2021-09-07 07:30:08

by Aswath Govindraju

Subject: Re: [PATCH] usb: cdns3: fix race condition before setting doorbell

On 07/09/21 11:56 am, Pawel Laszczak wrote:
> From: Pawel Laszczak <[email protected]>
>
> For DEV_VER_V3 version there exist race condition between clearing
> ep_sts.EP_STS_TRBERR and setting ep_cmd.EP_CMD_DRDY bit.
> Setting EP_CMD_DRDY will be ignored by controller when
> EP_STS_TRBERR is set. So, between these two instructions we have
> a small time gap in which the EP_STSS_TRBERR can be set. In such case
> the transfer will not start after setting doorbell.
>
> Fixes: 7733f6c32e36 ("usb: cdns3: Add Cadence USB3 DRD Driver")
> cc: <[email protected]> # 5.12.x
> Signed-off-by: Pawel Laszczak <[email protected]>
> ---

Reviewed-by: Aswath Govindraju <[email protected]>
Tested-by: Aswath Govindraju <[email protected]>

> drivers/usb/cdns3/cdns3-gadget.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/drivers/usb/cdns3/cdns3-gadget.c b/drivers/usb/cdns3/cdns3-gadget.c
> index 80aaab159e58..e9769fab21ea 100644
> --- a/drivers/usb/cdns3/cdns3-gadget.c
> +++ b/drivers/usb/cdns3/cdns3-gadget.c
> @@ -1100,6 +1100,19 @@ static int cdns3_ep_run_stream_transfer(struct cdns3_endpoint *priv_ep,
> return 0;
> }
>
> +static void cdns3_rearm_drdy_if_needed(struct cdns3_endpoint *priv_ep)
> +{
> + struct cdns3_device *priv_dev = priv_ep->cdns3_dev;
> +
> + if (priv_dev->dev_ver < DEV_VER_V3)
> + return;
> +
> + if (readl(&priv_dev->regs->ep_sts) & EP_STS_TRBERR) {
> + writel(EP_STS_TRBERR, &priv_dev->regs->ep_sts);
> + writel(EP_CMD_DRDY, &priv_dev->regs->ep_cmd);
> + }
> +}
> +
> /**
> * cdns3_ep_run_transfer - start transfer on no-default endpoint hardware
> * @priv_ep: endpoint object
> @@ -1351,6 +1364,7 @@ static int cdns3_ep_run_transfer(struct cdns3_endpoint *priv_ep,
> /*clearing TRBERR and EP_STS_DESCMIS before seting DRDY*/
> writel(EP_STS_TRBERR | EP_STS_DESCMIS, &priv_dev->regs->ep_sts);
> writel(EP_CMD_DRDY, &priv_dev->regs->ep_cmd);
> + cdns3_rearm_drdy_if_needed(priv_ep);
> trace_cdns3_doorbell_epx(priv_ep->name,
> readl(&priv_dev->regs->ep_traddr));
> }
>