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

["Jianjun Wang (王建军)" <Jianjun.Wang@mediatek.com>]

On Wed, 2024-03-06 at 09:50 +0100, AngeloGioacchino Del Regno wrote:
> 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).

Does this only happen when the PCIe MAC is reset without resetting the
PHY? Is it related to the reset framework?

Thanks.
> 
> 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;
> > >   	}
> > >   
> 
> 
>