linux-kernel - Re: [PATCH v2] PCI: mediatek-gen3: Assert MAC reset only if PHY reset also present

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Date: Fri, 1 Mar 2024 10:06:33 +0100
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
To: Siddharth Vadapalli <s-vadapalli@...com>
Cc: linux-pci@...r.kernel.org, ryder.lee@...iatek.com,
 jianjun.wang@...iatek.com, lpieralisi@...nel.org, kw@...ux.com,
 robh@...nel.org, bhelgaas@...gle.com, p.zabel@...gutronix.de,
 matthias.bgg@...il.com, linux-mediatek@...ts.infradead.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 kernel@...labora.com, wenst@...omium.org, nfraprado@...labora.com
Subject: Re: [PATCH v2] PCI: mediatek-gen3: Assert MAC reset only if PHY reset
 also present

Il 01/03/24 07:42, Siddharth Vadapalli ha scritto:
> On Thu, Feb 29, 2024 at 10:24:49AM +0100, AngeloGioacchino Del Regno wrote:
>> Some SoCs have two PCI-Express controllers: in the case of MT8195,
>> one of them is using a dedicated PHY, but the other uses a combo PHY
>> that is shared with USB and in that case the PHY cannot be reset
>> from the PCIe driver, or USB functionality will be unable to resume.
>>
>> Resetting the PCIe MAC without also resetting the PHY will result in
>> a full system lockup at PCIe resume time and the only option to
>> resume operation is to hard reboot the system (with a PMIC cut-off).
>>
>> To resolve this issue, check if we've got both a PHY and a MAC reset
>> and, if not, never assert resets at PM suspend time: in that case,
>> the link is still getting powered down as both the clocks and the
>> power domains will go down anyway.
>>
>> Fixes: d537dc125f07 ("PCI: mediatek-gen3: Add system PM support")
>> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
>> ---
>>
>> Changes in v2:
>>   - Rebased over next-20240229
>>
>>   drivers/pci/controller/pcie-mediatek-gen3.c | 25 ++++++++++++++-------
>>   1 file changed, 17 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/pci/controller/pcie-mediatek-gen3.c b/drivers/pci/controller/pcie-mediatek-gen3.c
>> index 975b3024fb08..99b5d7a49be1 100644
>> --- a/drivers/pci/controller/pcie-mediatek-gen3.c
>> +++ b/drivers/pci/controller/pcie-mediatek-gen3.c
>> @@ -874,17 +874,26 @@ static int mtk_pcie_power_up(struct mtk_gen3_pcie *pcie)
>>   	return err;
>>   }
>>   
>> -static void mtk_pcie_power_down(struct mtk_gen3_pcie *pcie)
>> +static void mtk_pcie_power_down(struct mtk_gen3_pcie *pcie, bool is_suspend)
>>   {
>> +	bool suspend_reset_supported = pcie->mac_reset && pcie->phy_reset;
>> +
>>   	clk_bulk_disable_unprepare(pcie->num_clks, pcie->clks);
>>   
>>   	pm_runtime_put_sync(pcie->dev);
>>   	pm_runtime_disable(pcie->dev);
>> -	reset_control_assert(pcie->mac_reset);
>> +
>> +	/*
>> +	 * Assert MAC reset only if we also got a PHY reset, otherwise
>> +	 * the system will lockup at PM resume time.
>> +	 */
>> +	if (is_suspend && suspend_reset_supported)
>> +		reset_control_assert(pcie->mac_reset);
>>   
>>   	phy_power_off(pcie->phy);
>>   	phy_exit(pcie->phy);
> 
> Wouldn't this power off the shared PHY? Or will the PHY driver make this
> NO-OP if the PHY is shared, in which case the above two statements could
> be combined with the other statements in the:
> if (is_suspend && suspend_reset_supported)
> condition to get a single block of code that also combines the
> reset_control_assert(pcie->phy_reset)
> present below.
> 

No, that'd be fine:

static int mtk_phy_power_off(struct phy *phy)
{
	struct mtk_phy_instance *instance = phy_get_drvdata(phy);
	struct mtk_tphy *tphy = dev_get_drvdata(phy->dev.parent);

	if (instance->type == PHY_TYPE_USB2)
		u2_phy_instance_power_off(tphy, instance);
	else if (instance->type == PHY_TYPE_PCIE)
		pcie_phy_instance_power_off(tphy, instance);

	return 0;
}

..it's two different PHY instances that we're dealing with, here :-)

Cheers,
Angelo

>> -	reset_control_assert(pcie->phy_reset);
>> +	if (is_suspend && suspend_reset_supported)
>> +		reset_control_assert(pcie->phy_reset);
>>   }
>>   
> ...
> 
> Regards,
> Siddharth.