[PATCH] CS5536: fix overly optimistic cable detect (handle libataAPI imprecision).

[Andreas Mohr]

We unconditionally indicated 80-pin cable capability
in case *any* of Master/Slave devices had 80c cable presence
configure-indicated by the BIOS.
This, however, does not seem at all appropriate since CS5536
does manage its primary IDE's master/slave devices independently,
both in cable detect and timing programming.
Since libata does not offer API support for such per-device
configurations yet, we really need to restrict things to the lowest
common denominator.

Signed-off-by: Andreas Mohr <andim2@xxxxxxxxxxxx>
---
 drivers/ata/pata_cs5536.c | 34 +++++++++++++++++++++++++++++++---
 1 Datei geändert, 31 Zeilen hinzugefügt(+), 3 Zeilen entfernt(-)

diff --git a/drivers/ata/pata_cs5536.c b/drivers/ata/pata_cs5536.c
index 0448860..f58bf04 100644
--- a/drivers/ata/pata_cs5536.c
+++ b/drivers/ata/pata_cs5536.c
@@ -146,10 +146,38 @@ static int cs5536_cable_detect(struct ata_port *ap)
 
 	cs5536_read(pdev, CFG, &cfg);
 
-	if (cfg & IDE_CFG_CABLE)
-		return ATA_CBL_PATA80;
-	else
+	/*
+	 * FIXME libata API limitation:
+	 * CS5536 data sheet says
+	 * "The IDE interface timing is completely programmable.
+	 * Timing control covers the command active and recover pulse
+	 * widths, and command block register accesses. The IDE
+	 * data transfer speed for each device on each channel can
+	 * be independently programmed allowing high speed IDE
+	 * peripherals to co-exist on the same channel as older,
+	 * compatible devices." and it does have per-drive-separate
+	 * cable detect and timing programming bits for primary Master/Slave
+	 * and in fact some devices (e.g. PCM-9375) do have e.g.
+	 * directly-soldered (read: ~80c) CompactFlash primary Master
+	 * and a 44pin (read: 40c) IDE primary Slave.
+	 * However, libata only offers whole-ata_port cable detect callback
+	 * that's arguably too imprecise for such hardware capabilities.
+	 * Given this imprecision, we arguably are required for now
+	 * to indicate the lowest common denominator, i.e. 40c in case
+	 * *any* of Master/Slave does not indicate 80c support,
+	 * in order to avoid imposing incorrect timing to the
+	 * per-device-separate timing programming.
+	 * This care seems especially important given evidence of
+	 * existing other timing issues of CS5536:
+	 * see errata 47 "UDMA Mode 5 stability issues" in PDF
+	 * "AMD Geode (tm) CS5536 Companion Device Silicon Revision B1
+	 * Specification Update".
+	 */
+	bool have_any_40c_only_device = (cfg & IDE_CFG_CABLE) < IDE_CFG_CABLE;
+	if (have_any_40c_only_device)
 		return ATA_CBL_PATA40;
+	else
+		return ATA_CBL_PATA80;
 }
 
 /**
-- 
1.7.11.7

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