Re: [PATCHv4 26/28] PCI: mobiveil: ls_pcie_g4: add Workaround for A-011451

[Bjorn Helgaas <helgaas@kernel.org>]

On Tue, Mar 12, 2019 at 09:34:17AM +0000, Z.q. Hou wrote:
> Hi Bjorn,
> 
> Thanks a lot for your comments!
> 
> > -----Original Message-----
> > From: Bjorn Helgaas [mailto:helgaas@kernel.org]
> > Sent: 2019年3月12日 1:35
> > To: Z.q. Hou <zhiqiang.hou@nxp.com>
> > Cc: linux-pci@vger.kernel.org; linux-arm-kernel@lists.infradead.org;
> > devicetree@vger.kernel.org; linux-kernel@vger.kernel.org;
> > robh+dt@kernel.org; mark.rutland@arm.com; l.subrahmanya@mobiveil.co.in;
> > shawnguo@kernel.org; Leo Li <leoyang.li@nxp.com>;
> > lorenzo.pieralisi@arm.com; catalin.marinas@arm.com;
> > will.deacon@arm.com; Mingkai Hu <mingkai.hu@nxp.com>; M.h. Lian
> > <minghuan.lian@nxp.com>; Xiaowei Bao <xiaowei.bao@nxp.com>
> > Subject: Re: [PATCHv4 26/28] PCI: mobiveil: ls_pcie_g4: add Workaround for
> > A-011451
> > 
> > On Mon, Mar 11, 2019 at 09:33:32AM +0000, Z.q. Hou wrote:
> > > From: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
> > >
> > > When LX2 PCIe controller is sending multiple split completions and ACK
> > > latency expires indicating that ACK should be send at priority.
> > > But because of large number of split completions and FC update DLLP,
> > > the controller does not give priority to ACK transmission. This
> > > results into ACK latency timer timeout error at the link partner and
> > > the pending TLPs are replayed by the link partner again.
> > >
> > > Workaround:
> > > 1. Reduce the ACK latency timeout value to a very small value.
> > > 2. Restrict the number of completions from the LX2 PCIe controller
> > >    to 1, by changing the Max Read Request Size (MRRS) of link partner
> > >    to the same value as Max Packet size (MPS).
> > >
> > > This patch implemented part 1, the part 2 can be set by kernel
> > > parameter 'pci=pcie_bus_perf'
> > 
> > If I understand correctly, you're saying that LX2160A Rev1.0 will only work
> > correctly if you have this patch applied AND you boot with
> > "pci=pcie_bus_perf".
> 
> Your understanding is correct.
> 
> > That might be OK if these rev 1.0 parts are only used in the lab and are never
> > shipped to customers.  But if these parts are ever shipped to customers, I
> > don't think it's acceptable for them to have to figure out that they must boot
> > with "pci=pcie_bus_perf".  Yes, you can document that in release notes, but
> > it's still a poor user experience, and users will forget, and they will see
> > mysterious hard-to-debug issues.

Since you didn't respond here, I assume these rev 1.0 parts have been
or will be shipped to end users?  Please confirm.

> > Maybe there's a way for you to automatically set that pcie_bus_perf mode?
> > With a dmesg note to indicate that you're overriding any mode the user may
> > have selected?
> 
> Actually we don't have a way to set the pcie_bus_perf automatically
> under Linux, we give this parameter in kernel cmdline.  Do you have
> any advice about how to set this parameter automatically under
> Linux?

The beauty of Linux being open-source is that if you need something
that doesn't exist, you are empowered to create it.

We do have one place already (cns3xxx_pcie_hw_init()) that explicitly
sets pcie_bus_config.  You might be able to do something similar.

> > > This ERRATA is only for LX2160A Rev1.0, and it will be fixed in
> > > Rev2.0.
> > >
> > > Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
> > > ---
> > > V4:
> > >  - no change
> > >
> > >  .../pci/controller/mobiveil/pci-layerscape-gen4.c | 15 +++++++++++++++
> > >  drivers/pci/controller/mobiveil/pcie-mobiveil.h   |  4 ++++
> > >  2 files changed, 19 insertions(+)
> > >
> > > diff --git a/drivers/pci/controller/mobiveil/pci-layerscape-gen4.c
> > > b/drivers/pci/controller/mobiveil/pci-layerscape-gen4.c
> > > index d2c5dbbd5e3c..20ce146788ca 100644
> > > --- a/drivers/pci/controller/mobiveil/pci-layerscape-gen4.c
> > > +++ b/drivers/pci/controller/mobiveil/pci-layerscape-gen4.c
> > > @@ -82,12 +82,27 @@ static bool ls_pcie_g4_is_bridge(struct ls_pcie_g4
> > *pcie)
> > >  	return header_type == PCI_HEADER_TYPE_BRIDGE;  }
> > >
> > > +static void workaround_A011451(struct ls_pcie_g4 *pcie) {
> > > +	struct mobiveil_pcie *mv_pci = pcie->pci;
> > > +	u32 val;
> > > +
> > > +	/* Set ACK latency timeout */
> > > +	val = csr_readl(mv_pci, GPEX_ACK_REPLAY_TO);
> > > +	val &= ~(ACK_LAT_TO_VAL_MASK << ACK_LAT_TO_VAL_SHIFT);
> > > +	val |= (4 << ACK_LAT_TO_VAL_SHIFT);
> > > +	csr_writel(mv_pci, val, GPEX_ACK_REPLAY_TO); }
> > > +
> > >  static int ls_pcie_g4_host_init(struct mobiveil_pcie *pci)  {
> > >  	struct ls_pcie_g4 *pcie = to_ls_pcie_g4(pci);
> > >
> > >  	pcie->rev = csr_readb(pci, PCI_REVISION_ID);
> > >
> > > +	if (pcie->rev == REV_1_0)
> > > +		workaround_A011451(pcie);
> > > +
> > >  	return 0;
> > >  }
> > >
> > > diff --git a/drivers/pci/controller/mobiveil/pcie-mobiveil.h
> > > b/drivers/pci/controller/mobiveil/pcie-mobiveil.h
> > > index ab43de5e4b2b..f0e2e4ae09b5 100644
> > > --- a/drivers/pci/controller/mobiveil/pcie-mobiveil.h
> > > +++ b/drivers/pci/controller/mobiveil/pcie-mobiveil.h
> > > @@ -85,6 +85,10 @@
> > >  #define PAB_AXI_AMAP_PEX_WIN_H(win)	PAB_REG_ADDR(0x0bac,
> > win)
> > >  #define PAB_INTP_AXI_PIO_CLASS		0x474
> > >
> > > +#define GPEX_ACK_REPLAY_TO		0x438
> > > +#define  ACK_LAT_TO_VAL_MASK		0x1fff
> > > +#define  ACK_LAT_TO_VAL_SHIFT		0
> > > +
> > >  #define PAB_PEX_AMAP_CTRL(win)		PAB_REG_ADDR(0x4ba0,
> > win)
> > >  #define  AMAP_CTRL_EN_SHIFT		0
> > >  #define  AMAP_CTRL_TYPE_SHIFT		1
> > > --
> > > 2.17.1
> > >
> 
> Thanks,
> Zhiqiang