mvebu: PCI: aardvark: Implement workaround for PCIe Completion Timeout

Turris MOX randomly crashes up, when there is connected miniPCIe card
MediaTek MT7915 with the following output:

[   71.457007] Internal error: synchronous external abort: 96000210 [#1] SMP
[   71.464021] Modules linked in: xt_connlimit pppoe ppp_async nf_conncount iptable_nat ath9k xt_state xt_nat xt_helper xt_conntrack xt_connmark xt_connbytes xt_REDIREl
[   71.464187]  btintel br_netfilter bnep bluetooth ath9k_hw ath10k_pci ath10k_core ath sch_tbf sch_ingress sch_htb sch_hfsc em_u32 cls_u32 cls_tcindex cls_route cls_mg
[   71.629589] CPU: 0 PID: 1298 Comm: kworker/u5:3 Not tainted 5.4.114 #0
[   71.636319] Hardware name: CZ.NIC Turris Mox Board (DT)
[   71.641725] Workqueue: napi_workq napi_workfn
[   71.646221] pstate: 80400085 (Nzcv daIf +PAN -UAO)
[   71.651169] pc : mt76_set_irq_mask+0x118/0x150 [mt76]
[   71.656385] lr : mt7915_init_debugfs+0x358/0x368 [mt7915e]
[   71.662038] sp : ffffffc010003cd0
[   71.665451] x29: ffffffc010003cd0 x28: 0000000000000060
[   71.670929] x27: ffffffc010a56f98 x26: ffffffc010c0fa9a
[   71.676407] x25: ffffffc010ba8788 x24: ffffff803e01fe00
[   71.681885] x23: 0000000000000030 x22: ffffffc010003dc4
[   71.687361] x21: 0000000000000000 x20: ffffff803e01fea4
[   71.692839] x19: ffffff803cb725c0 x18: 000000002d660780
[   71.698317] x17: 0000000000000000 x16: 0000000000000001
[   71.703795] x15: 0000000000005ee0 x14: ffffffc010d1d000
[   71.709272] x13: 0000000000002f70 x12: 0000000000000000
[   71.714749] x11: 0000000000000000 x10: 0000000000000040
[   71.720226] x9 : ffffffc010bbe980 x8 : ffffffc010bbe978
[   71.725704] x7 : ffffff803e4003f0 x6 : 0000000000000000
[   71.731181] x5 : ffffffc02f240000 x4 : ffffffc010003e00
[   71.736658] x3 : 0000000000000000 x2 : ffffffc008e3f230
[   71.742135] x1 : 00000000000d7010 x0 : ffffffc0114d7010
[   71.747613] Call trace:
[   71.750137]  mt76_set_irq_mask+0x118/0x150 [mt76]
[   71.754990]  mt7915_dual_hif_set_irq_mask+0x108/0xdc0 [mt7915e]
[   71.761098]  __handle_irq_event_percpu+0x6c/0x170
[   71.765950]  handle_irq_event_percpu+0x34/0x88
[   71.770531]  handle_irq_event+0x40/0xb0
[   71.774486]  handle_level_irq+0xe0/0x170
[   71.778530]  generic_handle_irq+0x24/0x38
[   71.782667]  advk_pcie_irq_handler+0x11c/0x238
[   71.787249]  __handle_irq_event_percpu+0x6c/0x170
[   71.792099]  handle_irq_event_percpu+0x34/0x88
[   71.796680]  handle_irq_event+0x40/0xb0
[   71.800633]  handle_fasteoi_irq+0xdc/0x190
[   71.804855]  generic_handle_irq+0x24/0x38
[   71.808988]  __handle_domain_irq+0x60/0xb8
[   71.813213]  gic_handle_irq+0x8c/0x198
[   71.817077]  el1_irq+0xf0/0x1c0
[   71.820314]  el1_da+0xc/0xc0
[   71.823288]  mt76_set_irq_mask+0x118/0x150 [mt76]
[   71.828141]  mt7915_mac_tx_free+0x4c4/0x828 [mt7915e]
[   71.833352]  mt7915_queue_rx_skb+0x5c/0xa8 [mt7915e]
[   71.838473]  mt76_dma_cleanup+0x89c/0x1248 [mt76]
[   71.843329]  __napi_poll+0x38/0xf8
[   71.846835]  napi_workfn+0x58/0xb0
[   71.850342]  process_one_work+0x1fc/0x390
[   71.854475]  worker_thread+0x48/0x4d0
[   71.858252]  kthread+0x120/0x128
[   71.861581]  ret_from_fork+0x10/0x1c
[   71.865273] Code: 52800000 d65f03c0 f9562c00 8b214000 (b9400000)
[   71.871560] ---[ end trace 1d4e29987011411b ]---
[   71.876320] Kernel panic - not syncing: Fatal exception in interrupt
[   71.882875] SMP: stopping secondary CPUs
[   71.886923] Kernel Offset: disabled
[   71.890519] CPU features: 0x0002,00002008
[   71.894649] Memory Limit: none
[   71.897799] Rebooting in 3 seconds..

Patch is awaiting upstream merge:
https://lore.kernel.org/linux-pci/20220802123816.21817-1-pali@kernel.org/T/#u

There was also discussion about it in the linux-pci mailing list, where can
be found response from Marvell's employee regarding A3720 PCIe erratum 3.12, which seems to provide further details which help this issue:
https://lore.kernel.org/linux-pci/BN9PR18MB425154FE5019DCAF2028A1D5DB8D9@BN9PR18MB4251.namprd18.prod.outlook.com/t/#u

Reported-by: Ondřej Caletka <ondrej@caletka.cz> [Turris MOX]
Signed-off-by: Josef Schlehofer <pepe.schlehofer@gmail.com>
Reviewed-by: Robert Marko <robimarko@gmail.com>

1 files changed, 81 insertions, 0 deletions

diff --git a/target/linux/mvebu/patches-5.15/100-aardvark-workaround-PCIe.patch b/target/linux/mvebu/patches-5.15/100-aardvark-workaround-PCIe.patch
new file mode 100644
index 0000000000..975eadb80e
--- /dev/null
+++ b/target/linux/mvebu/patches-5.15/100-aardvark-workaround-PCIe.patch
@@ -0,0 +1,81 @@
+Subject: [PATCH v2] PCI: aardvark: Implement workaround for PCIe Completion Timeout
+Date:   Tue,  2 Aug 2022 14:38:16 +0200
+Message-Id: <20220802123816.21817-1-pali@kernel.org>
+X-Mailer: git-send-email 2.20.1
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+Precedence: bulk
+List-ID: <linux-pci.vger.kernel.org>
+X-Mailing-List: linux-pci@vger.kernel.org
+
+Marvell Armada 3700 Functional Errata, Guidelines, and Restrictions
+document describes in erratum 3.12 PCIe Completion Timeout (Ref #: 251),
+that PCIe IP does not support a strong-ordered model for inbound posted vs.
+outbound completion.
+
+As a workaround for this erratum, DIS_ORD_CHK flag in Debug Mux Control
+register must be set. It disables the ordering check in the core between
+Completions and Posted requests received from the link.
+
+Marvell also suggests to do full memory barrier at the beginning of
+aardvark summary interrupt handler before calling interrupt handlers of
+endpoint drivers in order to minimize the risk for the race condition
+documented in the Erratum between the DMA done status reading and the
+completion of writing to the host memory.
+
+More details about this issue and suggested workarounds are in discussion:
+https://lore.kernel.org/linux-pci/BN9PR18MB425154FE5019DCAF2028A1D5DB8D9@BN9PR18MB4251.namprd18.prod.outlook.com/t/#u
+
+It was reported that enabling this workaround fixes instability issues and
+"Unhandled fault" errors when using 60 GHz WiFi 802.11ad card with Qualcomm
+QCA6335 chip under significant load which were caused by interrupt status
+stuck in the outbound CMPLT queue traced back to this erratum.
+
+This workaround fixes also kernel panic triggered after some minutes of
+usage 5 GHz WiFi 802.11ax card with Mediatek MT7915 chip:
+
+    Internal error: synchronous external abort: 96000210 [#1] SMP
+    Kernel panic - not syncing: Fatal exception in interrupt
+
+Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
+Signed-off-by: Pali Rohár <pali@kernel.org>
+Fixes: 8c39d710363c ("PCI: aardvark: Add Aardvark PCI host controller driver")
+Cc: stable@vger.kernel.org
+---
+ drivers/pci/controller/pci-aardvark.c | 10 ++++++++++
+ 1 file changed, 10 insertions(+)
+
+--- a/drivers/pci/controller/pci-aardvark.c
++++ b/drivers/pci/controller/pci-aardvark.c
+@@ -210,6 +210,8 @@ enum {
+ };
+ 
+ #define VENDOR_ID_REG				(LMI_BASE_ADDR + 0x44)
++#define DEBUG_MUX_CTRL_REG			(LMI_BASE_ADDR + 0x208)
++#define     DIS_ORD_CHK				BIT(30)
+ 
+ /* PCIe core controller registers */
+ #define CTRL_CORE_BASE_ADDR			0x18000
+@@ -558,6 +560,11 @@ static void advk_pcie_setup_hw(struct ad
+ 		PCIE_CORE_CTRL2_TD_ENABLE;
+ 	advk_writel(pcie, reg, PCIE_CORE_CTRL2_REG);
+ 
++	/* Disable ordering checks, workaround for erratum 3.12 "PCIe completion timeout" */
++	reg = advk_readl(pcie, DEBUG_MUX_CTRL_REG);
++	reg |= DIS_ORD_CHK;
++	advk_writel(pcie, reg, DEBUG_MUX_CTRL_REG);
++
+ 	/* Set lane X1 */
+ 	reg = advk_readl(pcie, PCIE_CORE_CTRL0_REG);
+ 	reg &= ~LANE_CNT_MSK;
+@@ -1580,6 +1587,9 @@ static irqreturn_t advk_pcie_irq_handler
+ 	struct advk_pcie *pcie = arg;
+ 	u32 status;
+ 
++	/* Full memory barrier (ARM dsb sy), workaround for erratum 3.12 "PCIe completion timeout" */
++	mb();
++
+ 	status = advk_readl(pcie, HOST_CTRL_INT_STATUS_REG);
+ 	if (!(status & PCIE_IRQ_CORE_INT))
+ 		return IRQ_NONE;