* ks_dw_pcie_initiate_link_train() question
@ 2016-10-04 17:40 ` Bjorn Helgaas
0 siblings, 0 replies; 4+ messages in thread
From: Bjorn Helgaas @ 2016-10-04 17:40 UTC (permalink / raw)
To: Murali Karicheri; +Cc: linux-pci, linux-arm-kernel
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);
}
^ permalink raw reply [flat|nested] 4+ messages in thread
* ks_dw_pcie_initiate_link_train() question
@ 2016-10-04 17:40 ` Bjorn Helgaas
0 siblings, 0 replies; 4+ messages in thread
From: Bjorn Helgaas @ 2016-10-04 17:40 UTC (permalink / raw)
To: linux-arm-kernel
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);
}
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: ks_dw_pcie_initiate_link_train() question
2016-10-04 17:40 ` Bjorn Helgaas
@ 2016-10-04 21:52 ` Murali Karicheri
-1 siblings, 0 replies; 4+ messages in thread
From: Murali Karicheri @ 2016-10-04 21:52 UTC (permalink / raw)
To: Bjorn Helgaas; +Cc: linux-pci, linux-arm-kernel
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
^ permalink raw reply [flat|nested] 4+ messages in thread
* ks_dw_pcie_initiate_link_train() question
@ 2016-10-04 21:52 ` Murali Karicheri
0 siblings, 0 replies; 4+ messages in thread
From: Murali Karicheri @ 2016-10-04 21:52 UTC (permalink / raw)
To: linux-arm-kernel
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
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2016-10-04 21:52 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2016-10-04 17:40 ks_dw_pcie_initiate_link_train() question Bjorn Helgaas
2016-10-04 17:40 ` Bjorn Helgaas
2016-10-04 21:52 ` Murali Karicheri
2016-10-04 21:52 ` Murali Karicheri
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