Re: [PATCH] PCI: meson: Fix PERST# timing by asserting reset before LTSSM enable

Hi Ronald,
I see you submitted the patch. Last couple of days I've been fixing the
etherenet of my BPiCM4+Waveshare-io-base-b due to which I couldn't test
your patch any sooner. Now I got my ethernet working but now I couldn't
reproduce the issue *without* either of our patches!!!

Anyway it's proper to initialize PCIe with RESET Active but I think
meson_pcie_assert_reset(mp) will give sufficient time to PCIe devices
to complete the reset cycle.

---
 drivers/pci/controller/dwc/pci-meson.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/controller/dwc/pci-meson.c
b/drivers/pci/controller/dwc/pci-meson.c index 0694084f612..c28ab40c9ff
100644 --- a/drivers/pci/controller/dwc/pci-meson.c
+++ b/drivers/pci/controller/dwc/pci-meson.c
@@ -308,8 +308,8 @@ static int meson_pcie_start_link(struct dw_pcie
*pci) {
 	struct meson_pcie *mp = to_meson_pcie(pci);
 
-	meson_pcie_ltssm_enable(mp);
 	meson_pcie_assert_reset(mp);
+	meson_pcie_ltssm_enable(mp);
 
 	return 0;
 }
-- 
---
 drivers/pci/controller/dwc/pci-meson.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/controller/dwc/pci-meson.c
b/drivers/pci/controller/dwc/pci-meson.c index c28ab40c9ff..2ef75157530
100644 --- a/drivers/pci/controller/dwc/pci-meson.c
+++ b/drivers/pci/controller/dwc/pci-meson.c
@@ -308,7 +308,6 @@ static int meson_pcie_start_link(struct dw_pcie
*pci) {
 	struct meson_pcie *mp = to_meson_pcie(pci);
 
-	meson_pcie_assert_reset(mp);
 	meson_pcie_ltssm_enable(mp);
 
 	return 0;
@@ -362,6 +361,8 @@ static int meson_pcie_host_init(struct dw_pcie_rp
*pp) 
 	pp->bridge->ops = &meson_pci_ops;
 
+	meson_pcie_assert_reset(mp);
+
 	meson_set_max_payload(mp, MAX_PAYLOAD_SIZE);
 	meson_set_max_rd_req_size(mp, MAX_READ_REQ_SIZE);
 
-- 

...Gowtham


On Wed, 17 Jun 2026 05:06:27 +0530
gowtham <[email protected]> wrote:

> Hi,
> 
> As Neil suggested I moved the PCIe reset to init; I've updated the tag
> at
> https://github.com/GowthamKudupudi/linux/tree/meson-pcie-warm-reset-linux-7.0.y
> 
> Ronald, yes, I do think its proper to initialize PCIe with RESET
> Active. Anyway we need the reset *cycle*. Please submit your patch as
> well.
> 
> Thank you!
> 
> ...Gowtham
> 
> On Tue, 16 Jun 2026 08:06:02 +0200
> [email protected] wrote:
> 
> > On 6/15/26 12:34, Ronald Claveau wrote:  
> > > On 6/14/26 3:56 AM, Gowtham Kudupudi wrote:    
> > >> On warm reboot, the PCIe controller's LTSSM starts link training
> > >> immediately if PERST# is already deasserted from the previous
> > >> boot. The driver then pulses PERST# for only 500us, which is too
> > >> short to properly reset the endpoint device that has already
> > >> started training.
> > >>
> > >> Fix by moving the PERST# assert/deassert pulse BEFORE enabling
> > >> LTSSM, so the endpoint gets a clean reset cycle before link
> > >> training begins.
> > >>
> > >> This was found on Amlogic G12B (A311D) with NVMe on an M.2 slot.
> > >> Cold boot worked because POR held PERST# low; warm reboot did
> > >> not. The fix was confirmed on a Banana Pi CM4 with Waveshare IO
> > >> base board.
> > >>
> > >> Signed-off-by: Gowtham Kudupudi <[email protected]>
> > >> ---
> > >>   drivers/pci/controller/dwc/pci-meson.c | 2 +-
> > >>   1 file changed, 1 insertion(+), 1 deletion(-)
> > >>
> > >> diff --git a/drivers/pci/controller/dwc/pci-meson.c
> > >> b/drivers/pci/controller/dwc/pci-meson.c index
> > >> 5f8e2f4b3c12..3a7e9f1d5b8c 100644 ---
> > >> a/drivers/pci/controller/dwc/pci-meson.c +++
> > >> b/drivers/pci/controller/dwc/pci-meson.c @@ -310,8 +310,8 @@
> > >> static int meson_pcie_start_link(struct dw_pcie *pci) {
> > >>   	struct meson_pcie *mp = to_meson_pcie(pci);
> > >>   
> > >> +	meson_pcie_assert_reset(mp);
> > >>   	meson_pcie_ltssm_enable(mp);
> > >> -	meson_pcie_assert_reset(mp);    
> > 
> > I think this change is valid, other controllers resets PERST
> > in the host init callback, so either this or move to the
> > init callback.
> > 
> > Reviewed-by: Neil Armstrong <[email protected]>
> >   
> > >>   
> > >>   	return 0;
> > >>   }    
> > > 
> > > Hi Gowtham,
> > > 
> > > I have a patch [1] that I haven't submitted yet.
> > > This might be related to your issue, what do you think ?    
> > 
> > Ronald, This fix is valid, it's definitely better to probe the
> > driver with PERST asserted, please send it.
> > 
> > Neil
> >   
> > > 
> > > [1]
> > > https://github.com/rclaveau-tech/linux-khadas/commit/bee0a02d9756
> > >   
> >   
>

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From 852811b11795ee389ea6a953ed0db69b76722469 Mon Sep 17 00:00:00 2001
From: Gowtham Kudupudi <[email protected]>
Date: Sun, 14 Jun 2026 09:41:01 +0530
Subject: [PATCH 1/2] PCI: meson: Fix PERST# timing by asserting reset before
 LTSSM enable

On warm reboot, the PCIe controller's LTSSM starts link training
immediately if PERST# is already deasserted from the previous boot.
The driver then pulses PERST# for only 500us, which is too short to
properly reset the endpoint device that has already started training.

Fix by moving the PERST# assert/deassert pulse BEFORE enabling LTSSM,
so the endpoint gets a clean reset cycle before link training begins.

This was found on Amlogic G12B (A311D) with NVMe on an M.2 slot.
Cold boot worked because POR held PERST# low; warm reboot did not.
The fix was confirmed on a Banana Pi CM4 with Waveshare IO base board.

Signed-off-by: Gowtham Kudupudi <[email protected]>
---
 drivers/pci/controller/dwc/pci-meson.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/controller/dwc/pci-meson.c b/drivers/pci/controller/dwc/pci-meson.c
index 0694084f612..c28ab40c9ff 100644
--- a/drivers/pci/controller/dwc/pci-meson.c
+++ b/drivers/pci/controller/dwc/pci-meson.c
@@ -308,8 +308,8 @@ static int meson_pcie_start_link(struct dw_pcie *pci)
 {
 	struct meson_pcie *mp = to_meson_pcie(pci);
 
-	meson_pcie_ltssm_enable(mp);
 	meson_pcie_assert_reset(mp);
+	meson_pcie_ltssm_enable(mp);
 
 	return 0;
 }
-- 
2.54.0

From 1bcf2c787d72b2c25852cc598b1201510b4132b0 Mon Sep 17 00:00:00 2001
From: Gowtham Kudupudi <[email protected]>
Date: Wed, 17 Jun 2026 04:29:45 +0530
Subject: [PATCH 2/2] PCI: meson: pcie reset moved to meson_pcie_host_init

As per the Neil's suggestion, inititial PCIe reset is moved to init
to make it proper.

Signed-off-by: Gowtham Kudupudi <[email protected]>
---
 drivers/pci/controller/dwc/pci-meson.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/controller/dwc/pci-meson.c b/drivers/pci/controller/dwc/pci-meson.c
index c28ab40c9ff..2ef75157530 100644
--- a/drivers/pci/controller/dwc/pci-meson.c
+++ b/drivers/pci/controller/dwc/pci-meson.c
@@ -308,7 +308,6 @@ static int meson_pcie_start_link(struct dw_pcie *pci)
 {
 	struct meson_pcie *mp = to_meson_pcie(pci);
 
-	meson_pcie_assert_reset(mp);
 	meson_pcie_ltssm_enable(mp);
 
 	return 0;
@@ -362,6 +361,8 @@ static int meson_pcie_host_init(struct dw_pcie_rp *pp)
 
 	pp->bridge->ops = &meson_pci_ops;
 
+	meson_pcie_assert_reset(mp);
+
 	meson_set_max_payload(mp, MAX_PAYLOAD_SIZE);
 	meson_set_max_rd_req_size(mp, MAX_READ_REQ_SIZE);
 
-- 
2.54.0