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Date:   Tue, 12 Dec 2023 09:32:03 -0600
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Subject: Re: [PATCH 1/2] thunderbolt: Introduce tb_switch_reset_ports(),
 tb_port_reset() and usb4_port_reset()
To:     Mika Westerberg <mika.westerberg@linux.intel.com>,
        Sanath S <Sanath.S@amd.com>
Cc:     andreas.noever@gmail.com, michael.jamet@intel.com,
        YehezkelShB@gmail.com, linux-usb@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20231212140047.2021496-1-Sanath.S@amd.com>
 <20231212140047.2021496-2-Sanath.S@amd.com>
 <20231212152706.GG1074920@black.fi.intel.com>
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From:   Mario Limonciello <mario.limonciello@amd.com>
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On 12/12/2023 09:27, Mika Westerberg wrote:
> On Tue, Dec 12, 2023 at 07:30:46PM +0530, Sanath S wrote:
>> Introduce the tb_switch_reset_ports() function that resets the
>> downstream ports of a given switch. This helps us reset the USB4
>> links created by boot firmware during the init sequence.
>>
>> Introduce the tb_port_reset() helper function that resets the
>> given port.
>>
>> Introduce the usb4_port_reset() function that performs the DPR
>> of a given port. This function follows the CM guide specification 7.3
>>
>> Suggested-by: Mario Limonciello <mario.limonciello@amd.com>
>> Signed-off-by: Sanath S <Sanath.S@amd.com>
>> ---
>>   drivers/thunderbolt/switch.c  | 31 ++++++++++++++++++++++++++++
>>   drivers/thunderbolt/tb.h      |  2 ++
>>   drivers/thunderbolt/tb_regs.h |  1 +
>>   drivers/thunderbolt/usb4.c    | 39 +++++++++++++++++++++++++++++++++++
>>   4 files changed, 73 insertions(+)
>>
>> diff --git a/drivers/thunderbolt/switch.c b/drivers/thunderbolt/switch.c
>> index 44e9b09de47a..26ad6cc1ee91 100644
>> --- a/drivers/thunderbolt/switch.c
>> +++ b/drivers/thunderbolt/switch.c
>> @@ -626,6 +626,19 @@ int tb_port_unlock(struct tb_port *port)
>>   	return 0;
>>   }
>>   
>> +/**
>> + * tb_port_reset() - Reset downstream port
>> + * @port: Port to reset
>> + *
>> + * Helps to reconfigure the USB4 link by resetting the downstream port.
>> + *
>> + * Return: Returns 0 on success or an error code on failure.
>> + */
>> +static int tb_port_reset(struct tb_port *port)
>> +{
>> +	return usb4_port_reset(port);
>> +}
>> +
>>   static int __tb_port_enable(struct tb_port *port, bool enable)
>>   {
>>   	int ret;
>> @@ -1547,6 +1560,24 @@ static void tb_dump_switch(const struct tb *tb, const struct tb_switch *sw)
>>   	       regs->__unknown1, regs->__unknown4);
>>   }
>>   
>> +/**
>> + * tb_switch_reset_ports() - Reset downstream ports of switch.
>> + * @sw: Switch whose ports need to be reset.
>> + *
>> + * Return: Returns 0 on success or an error code on failure.
>> + */
>> +int tb_switch_reset_ports(struct tb_switch *sw)
>> +{
>> +	struct tb_port *port;
>> +	int ret = -EINVAL;
> 
> Why it returns -EINVAL? What if this is run for non-USB4 router?

This is a good point, but in the non USB4 case (default return) maybe 
it's better to be -ENODEV and in patch 2 be careful about the caller.

> 
>> +
>> +	tb_switch_for_each_port(sw, port) {
>> +		if (tb_port_is_null(port) && port->cap_usb4)
>> +			ret = tb_port_reset(port);
> 
> Should it stop here and return ret?

+1

> 
>> +	}
>> +	return ret;
>> +}
>> +
>>   /**
>>    * tb_switch_reset() - reconfigure route, enable and send TB_CFG_PKG_RESET
>>    * @sw: Switch to reset
>> diff --git a/drivers/thunderbolt/tb.h b/drivers/thunderbolt/tb.h
>> index e299e53473ae..f2687ec4ac53 100644
>> --- a/drivers/thunderbolt/tb.h
>> +++ b/drivers/thunderbolt/tb.h
>> @@ -797,6 +797,7 @@ void tb_switch_remove(struct tb_switch *sw);
>>   void tb_switch_suspend(struct tb_switch *sw, bool runtime);
>>   int tb_switch_resume(struct tb_switch *sw);
>>   int tb_switch_reset(struct tb_switch *sw);
>> +int tb_switch_reset_ports(struct tb_switch *sw);
>>   int tb_switch_wait_for_bit(struct tb_switch *sw, u32 offset, u32 bit,
>>   			   u32 value, int timeout_msec);
>>   void tb_sw_set_unplugged(struct tb_switch *sw);
>> @@ -1281,6 +1282,7 @@ struct tb_port *usb4_switch_map_usb3_down(struct tb_switch *sw,
>>   int usb4_switch_add_ports(struct tb_switch *sw);
>>   void usb4_switch_remove_ports(struct tb_switch *sw);
>>   
>> +int usb4_port_reset(struct tb_port *port);
>>   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);
>> diff --git a/drivers/thunderbolt/tb_regs.h b/drivers/thunderbolt/tb_regs.h
>> index 87e4795275fe..d49530bc0d53 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)
>> diff --git a/drivers/thunderbolt/usb4.c b/drivers/thunderbolt/usb4.c
>> index 4277733d0021..55f7c163bf84 100644
>> --- a/drivers/thunderbolt/usb4.c
>> +++ b/drivers/thunderbolt/usb4.c
>> @@ -1073,6 +1073,45 @@ void usb4_switch_remove_ports(struct tb_switch *sw)
>>   	}
>>   }
>>   
>> +/**
>> + * usb4_port_reset() - Reset USB4 downsteam port
>> + * @port: USB4 port to reset.
>> + *
>> + * Helps to reconfigure USB4 link by resetting downstream port.
>> + *
>> + * Return: Returns 0 on success or an error code on failure.
>> + */
>> +int usb4_port_reset(struct tb_port *port)
>> +{
>> +	int ret;
>> +	u32 val = 0;
> 
> Reverse christmas tree please:
> 
> u32 val = 0;
> int ret;
> 
>> +
>> +	ret = tb_port_read(port, &val, TB_CFG_PORT,
>> +			port->cap_usb4 + PORT_CS_19, 1);
>> +	if (ret)
>> +		return ret;
>> +
>> +	val = 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;
>> +
>> +	/* Wait for 10ms after requesting downstream port reset */
>> +	msleep(10);
> 
> Probably good to add a couple of more ms just in case. Also
> usleep_range()? (or fsleep()).

Sanath had it at 20 but I had suggested to align to spec.
For the wiggle room maybe usleep_range(10000, 15000)?

> 
>> +
>> +	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);
>> +
>> +	return ret;
>> +}
>> +
>>   /**
>>    * usb4_port_unlock() - Unlock USB4 downstream port
>>    * @port: USB4 port to unlock
>> -- 
>> 2.34.1