[RFC PATCH] AHCI: Workaround for ATAPI on buggy AHCI controller

[Marc C <marc.ceeeee@xxxxxxxxx>]

Hello Jeff,

I'm working with a proprietary but AHCI-compatible SATA controller that uses
the libata driver. Early versions of this controller have issues with processing
non-data ATAPI commands. A workaround was identified which requires some
register pokes in the command completion path of the driver. I don't expect to
push this patch upstream (yet). However, I would like to get some feedback
regarding the workaround, and check if the placement of the code is "acceptable"
or if there would be a better place to put it.

The workaround itself is rather simple: toggle the START bit immediately after a
non-data ATAPI command completes. The ST bit toggle would be performed within
atomic context in the AHCI port interrupt ISR.

Signed-off-by: Marc C <marc.ceeeee@xxxxxxxxx>
---
 linux/drivers/ata/libahci.c     |   26 ++++++++++++++++++++++++++
 linux/drivers/ata/libata-core.c |    6 ++++++
 2 files changed, 32 insertions(+)

diff --git a/linux/drivers/ata/libahci.c b/linux/drivers/ata/libahci.c
index f9eaa82..20b3a9a 100644
--- a/linux/drivers/ata/libahci.c
+++ b/linux/drivers/ata/libahci.c
@@ -2215,6 +2215,32 @@ void ahci_set_em_messages(struct ahci_host_priv *hpriv,
 }
 EXPORT_SYMBOL_GPL(ahci_set_em_messages);

+void ahci_apply_atapi_workaround(struct ata_queued_cmd *qc)
+{
+    if (!(qc->flags & ATA_QCFLAG_DMAMAP)) {
+        /*
+         * Non-data ATAPI commands need to kick the DMA engine
+         */
+        struct ata_port *ap = qc->ap;
+        void __iomem *port_mmio = ahci_port_base(ap);
+        u32 tmp = readl(port_mmio + PORT_CMD);
+
+        /* check if the HBA is idle */
+        if ((tmp & (PORT_CMD_START | PORT_CMD_LIST_ON)) != 0) {
+            /* setting HBA to idle */
+            tmp &= ~PORT_CMD_START;
+            writel(tmp, port_mmio + PORT_CMD);
+
+            /* wait for engine to stop */
+            do {
+                tmp = readl(port_mmio + PORT_CMD);
+            } while (tmp & PORT_CMD_LIST_ON);
+        }
+        ahci_start_engine(ap);
+    }
+}
+EXPORT_SYMBOL_GPL(ahci_apply_atapi_workaround);
+
 MODULE_AUTHOR("Jeff Garzik");
 MODULE_DESCRIPTION("Common AHCI SATA low-level routines");
 MODULE_LICENSE("GPL");
diff --git a/linux/drivers/ata/libata-core.c b/linux/drivers/ata/libata-core.c
index 4e73e1b..383de21 100644
--- a/linux/drivers/ata/libata-core.c
+++ b/linux/drivers/ata/libata-core.c
@@ -4827,6 +4827,12 @@ void ata_qc_complete(struct ata_queued_cmd *qc)
 {
     struct ata_port *ap = qc->ap;

+    if (ata_is_atapi(qc->tf.protocol)) {
+        void ahci_apply_atapi_workaround(struct ata_queued_cmd *qc);
+        ahci_apply_atapi_workaround(qc);
+    }
+
     /* XXX: New EH and old EH use different mechanisms to
      * synchronize EH with regular execution path.
      *
--
1.7.9.5




--
Regards,
Marc
marc.ceeeee@xxxxxxxxx
--
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