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

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Message-ID: <9920b298-4627-4323-b367-13ee94a83869@ti.com>
Date: Fri, 1 Mar 2024 15:25:24 +0530
From: Siddharth Vadapalli <s-vadapalli@...com>
To: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
CC: Siddharth Vadapalli <s-vadapalli@...com>, <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

On Fri, Mar 01, 2024 at 10:06:33AM +0100, AngeloGioacchino Del Regno wrote:
> 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 :-)

I didn't realize that it is handled separately. Thank you for clarifying!

Regards,
Siddharth.