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Message-ID: <c55f2c6e-1de8-4248-a52a-d6c9e49b565a@collabora.com>
Date: Wed, 6 Mar 2024 09:50:10 +0100
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Subject: Re: [PATCH v2] PCI: mediatek-gen3: Assert MAC reset only if PHY reset
 also present
To: =?UTF-8?B?Smlhbmp1biBXYW5nICjnjovlu7rlhpsp?= <Jianjun.Wang@mediatek.com>,
 "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>
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References: <20240229092449.580971-1-angelogioacchino.delregno@collabora.com>
 <30824df32636dec25b9a5972b1ee8de76b295feb.camel@mediatek.com>
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
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Il 01/03/24 03:48, Jianjun Wang (王建军) ha scritto:
> Hi Angelo,
> 
> Thanks for your patch.
> 
> On Thu, 2024-02-29 at 10:24 +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@collabora.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);
>> -	reset_control_assert(pcie->phy_reset);
>> +	if (is_suspend && suspend_reset_supported)
>> +		reset_control_assert(pcie->phy_reset);
>>   }
>>   
>>   static int mtk_pcie_setup(struct mtk_gen3_pcie *pcie)
>> @@ -920,7 +929,7 @@ static int mtk_pcie_setup(struct mtk_gen3_pcie
>> *pcie)
>>   	return 0;
>>   
>>   err_setup:
>> -	mtk_pcie_power_down(pcie);
>> +	mtk_pcie_power_down(pcie, false);
>>   
>>   	return err;
>>   }
>> @@ -951,7 +960,7 @@ static int mtk_pcie_probe(struct platform_device
>> *pdev)
>>   	err = pci_host_probe(host);
>>   	if (err) {
>>   		mtk_pcie_irq_teardown(pcie);
>> -		mtk_pcie_power_down(pcie);
>> +		mtk_pcie_power_down(pcie, false);
>>   		return err;
>>   	}
>>   
>> @@ -969,7 +978,7 @@ static void mtk_pcie_remove(struct
>> platform_device *pdev)
>>   	pci_unlock_rescan_remove();
>>   
>>   	mtk_pcie_irq_teardown(pcie);
>> -	mtk_pcie_power_down(pcie);
>> +	mtk_pcie_power_down(pcie, false);
> 
> Is there any reason not to reset the MAC and PHY when probe fails and
> driver removing? Some SoCs may not have MTCMOS to cut off their power,
> we need to assert the reset signal to save power in that case.
> 

Sorry for the late reply - yes, there is a reason.

On platforms needing this quirk, resetting at .remove() time will hang the
machine if the module is reinserted later (hence, .probe() called at a later
time).

Regards,
Angelo

> Thanks.
> 
>>   }
>>   
>>   static void mtk_pcie_irq_save(struct mtk_gen3_pcie *pcie)
>> @@ -1044,7 +1053,7 @@ static int mtk_pcie_suspend_noirq(struct device
>> *dev)
>>   	dev_dbg(pcie->dev, "entered L2 states successfully");
>>   
>>   	mtk_pcie_irq_save(pcie);
>> -	mtk_pcie_power_down(pcie);
>> +	mtk_pcie_power_down(pcie, true);
>>   
>>   	return 0;
>>   }
>> @@ -1060,7 +1069,7 @@ static int mtk_pcie_resume_noirq(struct device
>> *dev)
>>   
>>   	err = mtk_pcie_startup_port(pcie);
>>   	if (err) {
>> -		mtk_pcie_power_down(pcie);
>> +		mtk_pcie_power_down(pcie, false);
>>   		return err;
>>   	}
>>