[PATCH] ata: libahci: clear PxCLBU and PxFBU for AHCI_HFLAG_32BIT_ONLY

[Niklas Cassel <cassel@kernel.org>]

A user reported that commit 105c42566a55 ("ata: ahci: force 32-bit DMA for
JMicron JMB582/JMB585") made the JMicron JMB585 unusable on his board.

The failure is seen as soon as the ahci driver is probed, and booting with
iommu=off does not solve the problem.

Looking at the AHCI specification, PxCLBU and PxFBU are both read only '0'
for HBAs that do not support 64-bit addressing.

For HBAs that support 64-bit addressing, the registers are read write,
with a reset value that is Implementation Specific.

When using the AHCI_HFLAG_32BIT_ONLY flag, the HBA does support 64-bit
addressing, but we are simply setting a 32-bit DMA mask. Thus, in this
case, we need to explicitly clear the registers to 0.

Fixes: c7a42156d99b ("ahci: disable 64bit dma on sb600")
Reported-by: Roland Waltersson <roland.waltersson@netinsight.net>
Closes: https://lore.kernel.org/linux-ide/IA0PR17MB668730A4ECCD65F7A1DC3EDC9EB62@IA0PR17MB6687.namprd17.prod.outlook.com/
Signed-off-by: Niklas Cassel <cassel@kernel.org>
---
 drivers/ata/libahci.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/ata/libahci.c b/drivers/ata/libahci.c
index 6d72eb017b49..3a40ea926588 100644
--- a/drivers/ata/libahci.c
+++ b/drivers/ata/libahci.c
@@ -748,11 +748,25 @@ void ahci_start_fis_rx(struct ata_port *ap)
 	if (hpriv->cap & HOST_CAP_64)
 		writel((pp->cmd_slot_dma >> 16) >> 16,
 		       port_mmio + PORT_LST_ADDR_HI);
+	/*
+	 * On HBAs that do not support 64-bit addressing PxCLBU is read only,
+	 * however, when forcing a HBA that has CAP.S64A in 32-bit only mode,
+	 * the register is RW, and the reset value is Implementation Specific.
+	 */
+	else if (hpriv->flags & AHCI_HFLAG_32BIT_ONLY)
+		writel(0, port_mmio + PORT_LST_ADDR_HI);
 	writel(pp->cmd_slot_dma & 0xffffffff, port_mmio + PORT_LST_ADDR);
 
 	if (hpriv->cap & HOST_CAP_64)
 		writel((pp->rx_fis_dma >> 16) >> 16,
 		       port_mmio + PORT_FIS_ADDR_HI);
+	/*
+	 * On HBAs that do not support 64-bit addressing PxFBU is read only,
+	 * however, when forcing a HBA that has CAP.S64A in 32-bit only mode,
+	 * the register is RW, and the reset value is Implementation Specific.
+	 */
+	else if (hpriv->flags & AHCI_HFLAG_32BIT_ONLY)
+		writel(0, port_mmio + PORT_FIS_ADDR_HI);
 	writel(pp->rx_fis_dma & 0xffffffff, port_mmio + PORT_FIS_ADDR);
 
 	/* enable FIS reception */
-- 
2.55.0