linux-kernel - Re: [PATCH v2] thunderbolt: Explicitly enable lane adapter hotplug events at startup

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Date:   Fri, 23 Sep 2022 11:08:30 -0500
From:   "Limonciello, Mario" <mario.limonciello@....com>
To:     Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:     Andreas Noever <andreas.noever@...il.com>,
        Michael Jamet <michael.jamet@...el.com>,
        Yehezkel Bernat <YehezkelShB@...il.com>,
        Mehta Sanju <Sanju.Mehta@....com>, stable@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] thunderbolt: Explicitly enable lane adapter hotplug
 events at startup

On 9/23/2022 04:16, Mika Westerberg wrote:
> Hi Mario,
> 
> On Thu, Sep 22, 2022 at 11:07:29AM -0500, Mario Limonciello wrote:
>> Software that has run before the USB4 CM in Linux runs may have disabled
>> hotplug events for a given lane adapter.
>>
>> Other CMs such as that one distributed with Windows 11 will enable hotplug
>> events. Do the same thing in the Linux CM which fixes hotplug events on
>> "AMD Pink Sardine".
>>
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
>> ---
>> v1->v2:
>>   * Only send second patch as first was merged already
>>   * s/usb4_enable_hotplug/usb4_port_hotplug_enable/
>>   * Clarify intended users in documentation comment
>>   * Only call for lane adapters
>>   * Add stable tag
>>
>>   drivers/thunderbolt/switch.c  |  4 ++++
>>   drivers/thunderbolt/tb.h      |  1 +
>>   drivers/thunderbolt/tb_regs.h |  1 +
>>   drivers/thunderbolt/usb4.c    | 20 ++++++++++++++++++++
>>   4 files changed, 26 insertions(+)
>>
>> diff --git a/drivers/thunderbolt/switch.c b/drivers/thunderbolt/switch.c
>> index 77d7f07ca075..3213239d12c8 100644
>> --- a/drivers/thunderbolt/switch.c
>> +++ b/drivers/thunderbolt/switch.c
>> @@ -778,6 +778,10 @@ static int tb_init_port(struct tb_port *port)
>>   
>>   			if (!tb_port_read(port, &hop, TB_CFG_HOPS, 0, 2))
>>   				port->ctl_credits = hop.initial_credits;
>> +
>> +			res = usb4_port_hotplug_enable(port);
>> +			if (res)
> 
> I think this does not belong here in tb_init_port(). This is called from
> both FW and SW CM paths and we don't want to confuse the FW CM more than
> necessary ;-)
> 
> So instead I think this should be added to tb_plug_events_active().
> 

The problem with that location is that tb_plug_events_active() is called 
from tb_switch_configure() which is before tb_switch_add() is called.
tb_switch_add() calls tb_init_port() which reads port->config for the 
first time.

So if this is only to be called in tb_switch_configure() it means 
reading port->config "earlier" too.

So it definitely needs to be called in tb_init_port() or a later 
function but before the device is announced to satisfy only running on 
the appropriate port types.

tb_init_port() or tb_switch_add feels like the right place to me.  How 
about leaving it where it is but guarding with a "if 
(!tb_switch_is_icm())" to avoid the risk to the FW CM case?

> Otherwise looks good to me.
> 
>> +				return res;
>>   		}
>>   		if (!port->ctl_credits)
>>   			port->ctl_credits = 2;
>> diff --git a/drivers/thunderbolt/tb.h b/drivers/thunderbolt/tb.h
>> index 5db76de40cc1..332159f984fc 100644
>> --- a/drivers/thunderbolt/tb.h
>> +++ b/drivers/thunderbolt/tb.h
>> @@ -1174,6 +1174,7 @@ int usb4_switch_add_ports(struct tb_switch *sw);
>>   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_configure(struct tb_port *port);
>>   void usb4_port_unconfigure(struct tb_port *port);
>>   int usb4_port_configure_xdomain(struct tb_port *port);
>> diff --git a/drivers/thunderbolt/tb_regs.h b/drivers/thunderbolt/tb_regs.h
>> index 166054110388..bbe38b2d9057 100644
>> --- a/drivers/thunderbolt/tb_regs.h
>> +++ b/drivers/thunderbolt/tb_regs.h
>> @@ -308,6 +308,7 @@ struct tb_regs_port_header {
>>   #define ADP_CS_5				0x05
>>   #define ADP_CS_5_LCA_MASK			GENMASK(28, 22)
>>   #define ADP_CS_5_LCA_SHIFT			22
>> +#define ADP_CS_5_DHP				BIT(31)
>>   
>>   /* TMU adapter registers */
>>   #define TMU_ADP_CS_3				0x03
>> diff --git a/drivers/thunderbolt/usb4.c b/drivers/thunderbolt/usb4.c
>> index 3a2e7126db9d..f0b5a8f1ed3a 100644
>> --- a/drivers/thunderbolt/usb4.c
>> +++ b/drivers/thunderbolt/usb4.c
>> @@ -1046,6 +1046,26 @@ int usb4_port_unlock(struct tb_port *port)
>>   	return tb_port_write(port, &val, TB_CFG_PORT, ADP_CS_4, 1);
>>   }
>>   
>> +/**
>> + * usb4_port_hotplug_enable() - Enables hotplug for a port
>> + * @port: USB4 port to operate on
>> + *
>> + * Enables hot plug events on a given port. This is only intended
>> + * to be used on lane, DP-IN, and DP-OUT adapters.
>> + */
>> +int usb4_port_hotplug_enable(struct tb_port *port)
>> +{
>> +	int ret;
>> +	u32 val;
>> +
>> +	ret = tb_port_read(port, &val, TB_CFG_PORT, ADP_CS_5, 1);
>> +	if (ret)
>> +		return ret;
>> +
>> +	val &= ~ADP_CS_5_DHP;
>> +	return tb_port_write(port, &val, TB_CFG_PORT, ADP_CS_5, 1);
>> +}
>> +
>>   static int usb4_port_set_configured(struct tb_port *port, bool configured)
>>   {
>>   	int ret;
>> -- 
>> 2.34.1