Received-SPF: pass (google.com: domain of linux-kernel+bounces-3360-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45e3:2400::1 as permitted sender) client-ip=2604:1380:45e3:2400::1;
Date: Mon, 18 Dec 2023 12:42:34 +0200
From: Mika Westerberg <mika.westerberg@linux.intel.com>
To: Sanath S <sanaths2@amd.com>
Cc: Sanath S <Sanath.S@amd.com>, mario.limonciello@amd.com,
	andreas.noever@gmail.com, michael.jamet@intel.com,
	YehezkelShB@gmail.com, linux-usb@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [Patch v2 2/2] thunderbolt: Teardown tunnels and reset
 downstream ports created by boot firmware
Message-ID: <20231218104234.GB1074920@black.fi.intel.com>
References: <20231213115256.GM1074920@black.fi.intel.com>
 <f673ffc8-f6f8-4898-d809-effb2c24e53e@amd.com>
 <20231214070746.GS1074920@black.fi.intel.com>
 <32163f49-8387-0754-534f-1764e731f26d@amd.com>
 <20231214073242.GT1074920@black.fi.intel.com>
 <ff143967-63ff-c4fb-9c88-8537a663c45b@amd.com>
 <20231215115521.GW1074920@black.fi.intel.com>
 <c7d174d3-028f-9ce4-7ef5-3e033c195159@amd.com>
 <20231215140224.GX1074920@black.fi.intel.com>
 <866cb714-b9a8-a7d4-4c59-6ba771ef325f@amd.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <866cb714-b9a8-a7d4-4c59-6ba771ef325f@amd.com>

On Mon, Dec 18, 2023 at 03:50:26PM +0530, Sanath S wrote:
> 
> On 12/15/2023 7:32 PM, Mika Westerberg wrote:
> > On Fri, Dec 15, 2023 at 07:24:07PM +0530, Sanath S wrote:
> > > On 12/15/2023 5:25 PM, Mika Westerberg wrote:
> > > > On Thu, Dec 14, 2023 at 09:00:29PM +0530, Sanath S wrote:
> > > > > > Unfortunately that's not possible because tb_switch_reset() lives in
> > > > > > switch.s (and should live there) and tb_deactivate_and_free_tunnel() is
> > > > > > part of tb.c (as should be). This is actually why I would like to try
> > > > > > the "reset" protocol adapters + their path config spaces in
> > > > > > tb_switch_reset() as then that would work with any router and does not
> > > > > > need to have any knowledge about tunnels or tb.c internals.
> > > > > Ok.
> > > > > To perform a protocol adapter reset we would require upstream and downstream
> > > > > adapter ports. So that we can use tb_port_write() set the ADP_PCIE_CS_0.Path
> > > > > Enable bits.
> > > > > Challenge here is to get the upstream port without discovering. I'll think
> > > > > more on this line
> > > > > if its possible to reset the protocol adapters and its path.
> > > > > 
> > > > > If you have any reference here or any idea already in mind, let me know, I
> > > > > can give it a try :)
> > > > Here is something I had in mind. Only build tested now, and not split
> > > > into proper patches. This would make it possible to reset any router if
> > > > we ever need that (not sure if we want to add the TBT2/3 bits now). Let
> > > > me know if you see problems with this.
> > > > 
> > > > Feel free to use this code as you like (or ignore completely).
> > > Thanks Mika for your suggestion.
> > > It looks good to me and I'll be checking this on Monday.
> > Okay.
> Unfortunately this is not working :(
> > > I have one doubt on protocol adapter reset part which I have mentioned
> > > below.
> > > > diff --git a/drivers/thunderbolt/domain.c b/drivers/thunderbolt/domain.c
> > > > index ec7b5f65804e..31f3da4e6a08 100644
> > > > --- a/drivers/thunderbolt/domain.c
> > > > +++ b/drivers/thunderbolt/domain.c
> > > > @@ -423,6 +423,7 @@ struct tb *tb_domain_alloc(struct tb_nhi *nhi, int timeout_msec, size_t privsize
> > > >    /**
> > > >     * tb_domain_add() - Add domain to the system
> > > >     * @tb: Domain to add
> > > > + * @reset: Issue reset to the host router
> > > >     *
> > > >     * Starts the domain and adds it to the system. Hotplugging devices will
> > > >     * work after this has been returned successfully. In order to remove
> > > > @@ -431,7 +432,7 @@ struct tb *tb_domain_alloc(struct tb_nhi *nhi, int timeout_msec, size_t privsize
> > > >     *
> > > >     * Return: %0 in case of success and negative errno in case of error
> > > >     */
> > > > -int tb_domain_add(struct tb *tb)
> > > > +int tb_domain_add(struct tb *tb, bool reset)
> > > >    {
> > > >    	int ret;
> > > > @@ -460,7 +461,7 @@ int tb_domain_add(struct tb *tb)
> > > >    	/* Start the domain */
> > > >    	if (tb->cm_ops->start) {
> > > > -		ret = tb->cm_ops->start(tb);
> > > > +		ret = tb->cm_ops->start(tb, reset);
> > > >    		if (ret)
> > > >    			goto err_domain_del;
> > > >    	}
> > > > diff --git a/drivers/thunderbolt/icm.c b/drivers/thunderbolt/icm.c
> > > > index d8b9c734abd3..623aa81a8833 100644
> > > > --- a/drivers/thunderbolt/icm.c
> > > > +++ b/drivers/thunderbolt/icm.c
> > > > @@ -2144,7 +2144,7 @@ static int icm_runtime_resume(struct tb *tb)
> > > >    	return 0;
> > > >    }
> > > > -static int icm_start(struct tb *tb)
> > > > +static int icm_start(struct tb *tb, bool not_used)
> > > >    {
> > > >    	struct icm *icm = tb_priv(tb);
> > > >    	int ret;
> > > > diff --git a/drivers/thunderbolt/lc.c b/drivers/thunderbolt/lc.c
> > > > index 633970fbe9b0..63cb4b6afb71 100644
> > > > --- a/drivers/thunderbolt/lc.c
> > > > +++ b/drivers/thunderbolt/lc.c
> > > > @@ -6,6 +6,8 @@
> > > >     * Author: Mika Westerberg <mika.westerberg@linux.intel.com>
> > > >     */
> > > > +#include <linux/delay.h>
> > > > +
> > > >    #include "tb.h"
> > > >    /**
> > > > @@ -45,6 +47,49 @@ static int find_port_lc_cap(struct tb_port *port)
> > > >    	return sw->cap_lc + start + phys * size;
> > > >    }
> > > > +/**
> > > > + * tb_lc_reset_port() - Trigger downstream port reset through LC
> > > > + * @port: Port that is reset
> > > > + *
> > > > + * Triggers downstream port reset through link controller registers.
> > > > + * Returns %0 in case of success negative errno otherwise. Only supports
> > > > + * non-USB4 routers with link controller (that's Thunderbolt 2 and
> > > > + * Thunderbolt 3).
> > > > + */
> > > > +int tb_lc_reset_port(struct tb_port *port)
> > > > +{
> > > > +	struct tb_switch *sw = port->sw;
> > > > +	int cap, ret;
> > > > +	u32 mode;
> > > > +
> > > > +	if (sw->generation < 2)
> > > > +		return -EINVAL;
> > > > +
> > > > +	cap = find_port_lc_cap(port);
> > > > +	if (cap < 0)
> > > > +		return cap;
> > > > +
> > > > +	ret = tb_sw_read(sw, &mode, TB_CFG_SWITCH, cap + TB_LC_PORT_MODE, 1);
> > > > +	if (ret)
> > > > +		return ret;
> > > > +
> > > > +	mode |= TB_LC_PORT_MODE_DPR;
> > > > +
> > > > +	ret = tb_sw_write(sw, &mode, TB_CFG_SWITCH, cap + TB_LC_PORT_MODE, 1);
> > > > +	if (ret)
> > > > +		return ret;
> > > > +
> > > > +	fsleep(10000);
> > > > +
> > > > +	ret = tb_sw_read(sw, &mode, TB_CFG_SWITCH, cap + TB_LC_PORT_MODE, 1);
> > > > +	if (ret)
> > > > +		return ret;
> > > > +
> > > > +	mode &= ~TB_LC_PORT_MODE_DPR;
> > > > +
> > > > +	return tb_sw_write(sw, &mode, TB_CFG_SWITCH, cap + TB_LC_PORT_MODE, 1);
> > > > +}
> > > > +
> > > >    static int tb_lc_set_port_configured(struct tb_port *port, bool configured)
> > > >    {
> > > >    	bool upstream = tb_is_upstream_port(port);
> > > > diff --git a/drivers/thunderbolt/nhi.c b/drivers/thunderbolt/nhi.c
> > > > index fb4f46e51753..b22023fae60d 100644
> > > > --- a/drivers/thunderbolt/nhi.c
> > > > +++ b/drivers/thunderbolt/nhi.c
> > > > @@ -1221,7 +1221,7 @@ static void nhi_check_iommu(struct tb_nhi *nhi)
> > > >    		str_enabled_disabled(port_ok));
> > > >    }
> > > > -static void nhi_reset(struct tb_nhi *nhi)
> > > > +static bool nhi_reset(struct tb_nhi *nhi)
> > > >    {
> > > >    	ktime_t timeout;
> > > >    	u32 val;
> > > > @@ -1229,11 +1229,11 @@ static void nhi_reset(struct tb_nhi *nhi)
> > > >    	val = ioread32(nhi->iobase + REG_CAPS);
> > > >    	/* Reset only v2 and later routers */
> > > >    	if (FIELD_GET(REG_CAPS_VERSION_MASK, val) < REG_CAPS_VERSION_2)
> > > > -		return;
> > > > +		return false;
> > > >    	if (!host_reset) {
> > > >    		dev_dbg(&nhi->pdev->dev, "skipping host router reset\n");
> > > > -		return;
> > > > +		return false;
> > > >    	}
> > > >    	iowrite32(REG_RESET_HRR, nhi->iobase + REG_RESET);
> > > > @@ -1244,12 +1244,14 @@ static void nhi_reset(struct tb_nhi *nhi)
> > > >    		val = ioread32(nhi->iobase + REG_RESET);
> > > >    		if (!(val & REG_RESET_HRR)) {
> > > >    			dev_warn(&nhi->pdev->dev, "host router reset successful\n");
> > > > -			return;
> > > > +			return true;
> > > >    		}
> > > >    		usleep_range(10, 20);
> > > >    	} while (ktime_before(ktime_get(), timeout));
> > > >    	dev_warn(&nhi->pdev->dev, "timeout resetting host router\n");
> > > > +
> > > > +	return false;
> > > >    }
> > > >    static int nhi_init_msi(struct tb_nhi *nhi)
> > > > @@ -1331,6 +1333,7 @@ static int nhi_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> > > >    	struct device *dev = &pdev->dev;
> > > >    	struct tb_nhi *nhi;
> > > >    	struct tb *tb;
> > > > +	bool reset;
> > > >    	int res;
> > > >    	if (!nhi_imr_valid(pdev))
> > > > @@ -1365,7 +1368,11 @@ static int nhi_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> > > >    	nhi_check_quirks(nhi);
> > > >    	nhi_check_iommu(nhi);
> > > > -	nhi_reset(nhi);
> > > > +	/*
> > > > +	 * Only USB4 v2 hosts support host reset so if we already did
> > > > +	 * that then don't do it again when the domain is initialized.
> > > > +	 */
> > > > +	reset = nhi_reset(nhi) ? false : host_reset;
> > > >    	res = nhi_init_msi(nhi);
> > > >    	if (res)
> > > > @@ -1392,7 +1399,7 @@ static int nhi_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> > > >    	dev_dbg(dev, "NHI initialized, starting thunderbolt\n");
> > > > -	res = tb_domain_add(tb);
> > > > +	res = tb_domain_add(tb, reset);
> > > >    	if (res) {
> > > >    		/*
> > > >    		 * At this point the RX/TX rings might already have been
> > > > diff --git a/drivers/thunderbolt/path.c b/drivers/thunderbolt/path.c
> > > > index 091a81bbdbdc..f760e54cd9bd 100644
> > > > --- a/drivers/thunderbolt/path.c
> > > > +++ b/drivers/thunderbolt/path.c
> > > > @@ -446,6 +446,19 @@ static int __tb_path_deactivate_hop(struct tb_port *port, int hop_index,
> > > >    	return -ETIMEDOUT;
> > > >    }
> > > > +/**
> > > > + * tb_path_deactivate_hop() - Deactivate one path in path config space
> > > > + * @port: Lane or protocol adapter
> > > > + * @hop_index: HopID of the path to be cleared
> > > > + *
> > > > + * This deactivates or clears a single path config space entry at
> > > > + * @hop_index. Returns %0 in success and negative errno otherwise.
> > > > + */
> > > > +int tb_path_deactivate_hop(struct tb_port *port, int hop_index)
> > > > +{
> > > > +	return __tb_path_deactivate_hop(port, hop_index, true);
> > > > +}
> > > > +
> > > >    static void __tb_path_deactivate_hops(struct tb_path *path, int first_hop)
> > > >    {
> > > >    	int i, res;
> > > > diff --git a/drivers/thunderbolt/switch.c b/drivers/thunderbolt/switch.c
> > > > index 900114ba4371..c4f486629a2b 100644
> > > > --- a/drivers/thunderbolt/switch.c
> > > > +++ b/drivers/thunderbolt/switch.c
> > > > @@ -676,6 +676,13 @@ int tb_port_disable(struct tb_port *port)
> > > >    	return __tb_port_enable(port, false);
> > > >    }
> > > > +static int tb_port_reset(struct tb_port *port)
> > > > +{
> > > > +	if (tb_switch_is_usb4(port->sw))
> > > > +		return usb4_port_reset(port);
> > > > +	return tb_lc_reset_port(port);
> > > > +}
> > > > +
> > > >    /*
> > > >     * tb_init_port() - initialize a port
> > > >     *
> > > > @@ -1532,20 +1539,64 @@ static void tb_dump_switch(const struct tb *tb, const struct tb_switch *sw)
> > > >    }
> > > >    /**
> > > > - * tb_switch_reset() - reconfigure route, enable and send TB_CFG_PKG_RESET
> > > > - * @sw: Switch to reset
> > > > + * tb_switch_reset() - Perform reset to the router
> > > > + * @sw: Router to reset
> > > >     *
> > > > - * Return: Returns 0 on success or an error code on failure.
> > > > + * Issues reset to the router. Can be used for any router. Returns %0
> > > > + * on success or an error code on failure.
> > > >     */
> > > >    int tb_switch_reset(struct tb_switch *sw)
> > > >    {
> > > >    	struct tb_cfg_result res;
> > > > -	if (sw->generation > 1)
> > > > -		return 0;
> > > > +	tb_sw_dbg(sw, "resetting router\n");
> > > > +
> > > > +	if (sw->generation > 1) {
> > > > +		struct tb_port *port;
> > > > +
> > > > +		tb_switch_for_each_port(sw, port) {
> > > > +			int i, ret;
> > > > +
> > > > +			/*
> > > > +			 * For lane adapters we issue downstream port
> > > > +			 * reset. That clears up also the path config
> > > > +			 * spaces.
> > > > +			 *
> > > > +			 * For protocol adapters we disable the path and
> > > > +			 * clear path config space one by one (from 8 to
> > > > +			 * Max Input HopID of the adapter).
> > > > +			 */
> > > > +			if (tb_port_is_null(port) && !tb_is_upstream_port(port)) {
> > > > +				ret = tb_port_reset(port);
> > > > +				if (ret)
> > > > +					return ret;
> > > > +				continue;
> > > I had thought in similar lines when you told about reset protocol adapters.
> > > 
> > > But, here we are traversing through all the ports, what if we get to perform
> > > the DPR first ?
> > > and then the PCIe, USB and DP reset. This may cause unplug event before we
> > > tear down
> > > protocol adapters and its path configuration. (I may be wrong)
> > Yeah, it could be that it is better first disable protocol adapters and
> > then do the DPR or so.
> I gave it a try doing a DPR later and before disabling protocol adapters.
> Both the methods didn't work.
> 
> However, when I do it like below, it works.
> 
>                 tb_switch_discover_tunnels(tb->root_switch,
>                          &tcm->tunnel_list, false);
>                 ret = tb_switch_reset(tb->root_switch);
> 
> We are missing something here.

The discover part should not do anything (like write the hardware) so
perhaps it is just some timing thing (but that's weird too).

I think we should do something like this:

1. Disable all enabled protocol adapters (reset them to defaults).
2. Clear all protocol adapter paths.
3. Issue DPR over all enabled USB4 ports.

BTW, what you mean "didn't work"?

> > > I'll check the behavior on Monday and update.
> > > 
> > > Assuming this works, I can incorporate the suggestion and send out v3 with
> > > appropriate tags ? It can be split into 3 patches.
> > Sure.
> > 
> > Bonus points if you can drop some more lines from that :)
> > 
> > > > +			} else if (tb_port_is_usb3_down(port) ||
> > > > +				   tb_port_is_usb3_up(port)) {
> > > > +				tb_usb3_port_enable(port, false);
> > > > +			} else if (tb_port_is_dpin(port) ||
> > > > +				   tb_port_is_dpout(port)) {
> > > > +				tb_dp_port_enable(port, false);
> > > > +			} else if (tb_port_is_pcie_down(port) ||
> > > > +				   tb_port_is_pcie_up(port)) {
> > > > +				tb_pci_port_enable(port, false);
> Here, as per spec it would be better if we first teardown it for DOWN path
> and then the UP
> path.

Right makes sense.

> > > > +			} else {
> > > > +				continue;
> > > > +			}
> > > > -	tb_sw_dbg(sw, "resetting switch\n");
> > > > +			/* Cleanup path config space of protocol adapter */
> > > > +			for (i = TB_PATH_MIN_HOPID;
> > > > +			     i <= port->config.max_in_hop_id; i++) {
> > > > +				ret = tb_path_deactivate_hop(port, i);
> > > > +				if (ret)
> > > > +					return ret;
> > > > +			}
> > > > +		}
> > > > +
> > > > +		return 0;
> > > > +	}
> > > > +	/* Thunderbolt 1 uses the "reset" config space packet */
> > > >    	res.err = tb_sw_write(sw, ((u32 *) &sw->config) + 2,
> > > >    			      TB_CFG_SWITCH, 2, 2);
> > > >    	if (res.err)
> > > > diff --git a/drivers/thunderbolt/tb.c b/drivers/thunderbolt/tb.c
> > > > index 8bc3985df749..5e5e3aebe018 100644
> > > > --- a/drivers/thunderbolt/tb.c
> > > > +++ b/drivers/thunderbolt/tb.c
> > > > @@ -2590,7 +2590,7 @@ static int tb_scan_finalize_switch(struct device *dev, void *data)
> > > >    	return 0;
> > > >    }
> > > > -static int tb_start(struct tb *tb)
> > > > +static int tb_start(struct tb *tb, bool reset)
> > > >    {
> > > >    	struct tb_cm *tcm = tb_priv(tb);
> > > >    	int ret;
> > > > @@ -2631,12 +2631,22 @@ static int tb_start(struct tb *tb)
> > > >    	tb_switch_tmu_configure(tb->root_switch, TB_SWITCH_TMU_MODE_LOWRES);
> > > >    	/* Enable TMU if it is off */
> > > >    	tb_switch_tmu_enable(tb->root_switch);
> > > > -	/* Full scan to discover devices added before the driver was loaded. */
> > > > -	tb_scan_switch(tb->root_switch);
> > > > -	/* Find out tunnels created by the boot firmware */
> > > > -	tb_discover_tunnels(tb);
> > > > -	/* Add DP resources from the DP tunnels created by the boot firmware */
> > > > -	tb_discover_dp_resources(tb);
> > > > +
> > > > +	if (reset && usb4_switch_version(tb->root_switch) == 1) {
> > > > +		ret = tb_switch_reset(tb->root_switch);
> > > > +		if (ret) {
> > > > +			tb_sw_warn(tb->root_switch, "failed to reset\n");
> > > > +			return ret;
> > > > +		}
> > > > +	
> > > Ok. So idea is to drop reset for <= TBT3 currently.
> > Yes, there are some older Apple systems that "benefit" from the
> > discovery so I would keep it there for them.
> > 
> > > > } else {
> > > > +		/* Full scan to discover devices added before the driver was loaded. */
> > > > +		tb_scan_switch(tb->root_switch);
> > > > +		/* Find out tunnels created by the boot firmware */
> > > > +		tb_discover_tunnels(tb);
> > > > +		/* Add DP resources from the DP tunnels created by the boot firmware */
> > > > +		tb_discover_dp_resources(tb);
> > > > +	}
> > > > +
> > > >    	/*
> > > >    	 * If the boot firmware did not create USB 3.x tunnels create them
> > > >    	 * now for the whole topology.
> > > > @@ -2702,7 +2712,7 @@ static int tb_resume_noirq(struct tb *tb)
> > > >    {
> > > >    	struct tb_cm *tcm = tb_priv(tb);
> > > >    	struct tb_tunnel *tunnel, *n;
> > > > -	unsigned int usb3_delay = 0;
> > > > +	unsigned int usb3_delay;
> > > >    	LIST_HEAD(tunnels);
> > > >    	tb_dbg(tb, "resuming...\n");
> > > > @@ -2715,19 +2725,7 @@ static int tb_resume_noirq(struct tb *tb)
> > > >    	tb_free_unplugged_children(tb->root_switch);
> > > >    	tb_restore_children(tb->root_switch);
> > > > -	/*
> > > > -	 * If we get here from suspend to disk the boot firmware or the
> > > > -	 * restore kernel might have created tunnels of its own. Since
> > > > -	 * we cannot be sure they are usable for us we find and tear
> > > > -	 * them down.
> > > > -	 */
> > > > -	tb_switch_discover_tunnels(tb->root_switch, &tunnels, false);
> > > > -	list_for_each_entry_safe_reverse(tunnel, n, &tunnels, list) {
> > > > -		if (tb_tunnel_is_usb3(tunnel))
> > > > -			usb3_delay = 500;
> > > > -		tb_tunnel_deactivate(tunnel);
> > > > -		tb_tunnel_free(tunnel);
> > > > -	}
> > > > +	usb3_delay = tb_switch_is_usb4(tb->root_switch) ? 500 : 0;
> > > >    	/* Re-create our tunnels now */
> > > >    	list_for_each_entry_safe(tunnel, n, &tcm->tunnel_list, list) {
> > > > diff --git a/drivers/thunderbolt/tb.h b/drivers/thunderbolt/tb.h
> > > > index 7ad55f5966f3..2bc8eca965ed 100644
> > > > --- a/drivers/thunderbolt/tb.h
> > > > +++ b/drivers/thunderbolt/tb.h
> > > > @@ -489,7 +489,7 @@ struct tb_path {
> > > >     */
> > > >    struct tb_cm_ops {
> > > >    	int (*driver_ready)(struct tb *tb);
> > > > -	int (*start)(struct tb *tb);
> > > > +	int (*start)(struct tb *tb, bool reset);
> > > >    	void (*stop)(struct tb *tb);
> > > >    	int (*suspend_noirq)(struct tb *tb);
> > > >    	int (*resume_noirq)(struct tb *tb);
> > > > @@ -752,7 +752,7 @@ int tb_xdomain_init(void);
> > > >    void tb_xdomain_exit(void);
> > > >    struct tb *tb_domain_alloc(struct tb_nhi *nhi, int timeout_msec, size_t privsize);
> > > > -int tb_domain_add(struct tb *tb);
> > > > +int tb_domain_add(struct tb *tb, bool reset);
> > > >    void tb_domain_remove(struct tb *tb);
> > > >    int tb_domain_suspend_noirq(struct tb *tb);
> > > >    int tb_domain_resume_noirq(struct tb *tb);
> > > > @@ -1156,6 +1156,7 @@ struct tb_path *tb_path_alloc(struct tb *tb, struct tb_port *src, int src_hopid,
> > > >    void tb_path_free(struct tb_path *path);
> > > >    int tb_path_activate(struct tb_path *path);
> > > >    void tb_path_deactivate(struct tb_path *path);
> > > > +int tb_path_deactivate_hop(struct tb_port *port, int hop_index);
> > > >    bool tb_path_is_invalid(struct tb_path *path);
> > > >    bool tb_path_port_on_path(const struct tb_path *path,
> > > >    			  const struct tb_port *port);
> > > > @@ -1175,6 +1176,7 @@ int tb_drom_read(struct tb_switch *sw);
> > > >    int tb_drom_read_uid_only(struct tb_switch *sw, u64 *uid);
> > > >    int tb_lc_read_uuid(struct tb_switch *sw, u32 *uuid);
> > > > +int tb_lc_reset_port(struct tb_port *port);
> > > >    int tb_lc_configure_port(struct tb_port *port);
> > > >    void tb_lc_unconfigure_port(struct tb_port *port);
> > > >    int tb_lc_configure_xdomain(struct tb_port *port);
> > > > @@ -1307,6 +1309,7 @@ void usb4_switch_remove_ports(struct tb_switch *sw);
> > > >    int usb4_port_unlock(struct tb_port *port);
> > > >    int usb4_port_hotplug_enable(struct tb_port *port);
> > > > +int usb4_port_reset(struct tb_port *port);
> > > >    int usb4_port_configure(struct tb_port *port);
> > > >    void usb4_port_unconfigure(struct tb_port *port);
> > > >    int usb4_port_configure_xdomain(struct tb_port *port, struct tb_xdomain *xd);
> > > > diff --git a/drivers/thunderbolt/tb_regs.h b/drivers/thunderbolt/tb_regs.h
> > > > index 87e4795275fe..efcae298b370 100644
> > > > --- a/drivers/thunderbolt/tb_regs.h
> > > > +++ b/drivers/thunderbolt/tb_regs.h
> > > > @@ -389,6 +389,7 @@ struct tb_regs_port_header {
> > > >    #define PORT_CS_18_CSA				BIT(22)
> > > >    #define PORT_CS_18_TIP				BIT(24)
> > > >    #define PORT_CS_19				0x13
> > > > +#define PORT_CS_19_DPR				BIT(0)
> > > >    #define PORT_CS_19_PC				BIT(3)
> > > >    #define PORT_CS_19_PID				BIT(4)
> > > >    #define PORT_CS_19_WOC				BIT(16)
> > > > @@ -584,6 +585,9 @@ struct tb_regs_hop {
> > > >    #define TB_LC_POWER				0x740
> > > >    /* Link controller registers */
> > > > +#define TB_LC_PORT_MODE				0x26
> > > > +#define TB_LC_PORT_MODE_DPR			BIT(0)
> > > > +
> > > >    #define TB_LC_CS_42				0x2a
> > > >    #define TB_LC_CS_42_USB_PLUGGED			BIT(31)
> > > > diff --git a/drivers/thunderbolt/usb4.c b/drivers/thunderbolt/usb4.c
> > > > index 675d1ed62372..9e002bf73d2e 100644
> > > > --- a/drivers/thunderbolt/usb4.c
> > > > +++ b/drivers/thunderbolt/usb4.c
> > > > @@ -1107,6 +1107,45 @@ int usb4_port_hotplug_enable(struct tb_port *port)
> > > >    	return tb_port_write(port, &val, TB_CFG_PORT, ADP_CS_5, 1);
> > > >    }
> > > > +/**
> > > > + * usb4_port_reset() - Issue downstream port reset
> > > > + * @port: USB4 port to reset
> > > > + *
> > > > + * Issues downstream port reset to @port.
> > > > + */
> > > > +int usb4_port_reset(struct tb_port *port)
> > > > +{
> > > > +	int ret;
> > > > +	u32 val;
> > > > +
> > > > +	if (!port->cap_usb4)
> > > > +		return -EINVAL;
> > > > +
> We've to drop this check here and check it before calling for that port.
> Otherwise, I it may throw -EINVAL and results in probe failure.

Agree.

> > > > +	ret = tb_port_read(port, &val, TB_CFG_PORT,
> > > > +			   port->cap_usb4 + PORT_CS_19, 1);
> > > > +	if (ret)
> > > > +		return ret;
> > > > +
> > > > +	val |= PORT_CS_19_DPR;
> > > > +
> > > > +	ret = tb_port_write(port, &val, TB_CFG_PORT,
> > > > +			    port->cap_usb4 + PORT_CS_19, 1);
> > > > +	if (ret)
> > > > +		return ret;
> > > > +
> > > > +	fsleep(10000);
> > > > +
> > > > +	ret = tb_port_read(port, &val, TB_CFG_PORT,
> > > > +			   port->cap_usb4 + PORT_CS_19, 1);
> > > > +	if (ret)
> > > > +		return ret;
> > > > +
> > > > +	val &= ~PORT_CS_19_DPR;
> > > > +
> > > > +	return tb_port_write(port, &val, TB_CFG_PORT,
> > > > +			     port->cap_usb4 + PORT_CS_19, 1);
> > > > +}
> > > > +
> > > >    static int usb4_port_set_configured(struct tb_port *port, bool configured)
> > > >    {
> > > >    	int ret;
> > > > 
> > > >