On 10/04/2016 01:40 PM, Bjorn Helgaas wrote:
> Hi Murali,
>
> This code looks suspicious. Can you comment?
>
> void ks_dw_pcie_initiate_link_train(struct keystone_pcie *ks_pcie)
> {
> u32 val;
>
> /* Disable Link training */
> val = readl(ks_pcie->va_app_base + CMD_STATUS);
> val &= ~LTSSM_EN_VAL;
> writel(LTSSM_EN_VAL | val, ks_pcie->va_app_base + CMD_STATUS);
>
> Here we cleared the LTSSM_EN_VAL bit in "val", but then we add it
> right back in before writing it back to CMD_STATUS.
>
> That looks like a cut and paste error to me, but of course I don't
> know the hardware.
>
> /* Initiate Link Training */
> val = readl(ks_pcie->va_app_base + CMD_STATUS);
> writel(LTSSM_EN_VAL | val, ks_pcie->va_app_base + CMD_STATUS);
> }
>
>
Bjorn,
Good catch! That is a cut-n-paste error. Here is the description from
device manual
================
Disable link training by de-asserting the LTSSM_EN bit in the PCIESS
Command Status Register (CMD_STATUS[LTSSM_EN]=0). Upon reset, the
LTSSM_EN is de-asserted automatically by hardware.
Initiate link training can be initiated by asserting LTSSM_EN bit in the
CMD_STATUS register (CMD_STATUS[LTSSM_EN]=1).
================================================
Probably it works because it is de-asserted automatically upon
reset by hardware. Let me test this and send you a patch?
--
Murali Karicheri
Linux Kernel, Keystone
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