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

[AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>]

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@xxxxxxxxxxxxx>
> > ---
> >
> > 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;
> >   	}
> >