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

From: Bjorn Helgaas <[email-masked]>
Date: Mon, 11 Mar 2019 12:34:39 -0500

On Mon, Mar 11, 2019 at 09:33:32AM +0000, Z.q. Hou wrote:
> From: Hou Zhiqiang <[email-masked]>
> 
> 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".

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.

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?

> This ERRATA is only for LX2160A Rev1.0, and it will be fixed
> in Rev2.0.
> 
> Signed-off-by: Hou Zhiqiang <[email-masked]>
> ---
> 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
> 

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