esp_scsi: correctly detect am53c974

The am53c974 returns the same ID as the FAS236, but implements
things slightly differently. So detect the am53c974 by checking
for ESP_CONFIG4 register.

Reviewed-by: Paolo Bonzini <[e-mail]>
Signed-off-by: Hannes Reinecke <[e-mail]>
Signed-off-by: Christoph Hellwig <[e-mail]>

drivers/scsi/am53c974.c

···
 	}
 	esp->scsi_id = EEbuf[DC390_EE_ADAPT_SCSI_ID];
 	esp->num_tags = 2 << EEbuf[DC390_EE_TAG_CMD_NUM];
+	if (EEbuf[DC390_EE_MODE2] & DC390_EE_MODE2_ACTIVE_NEGATION)
+		esp->config4 |= ESP_CONFIG4_RADE | ESP_CONFIG4_RAE;
 }
 
 static int pci_esp_probe_one(struct pci_dev *pdev,

drivers/scsi/esp_scsi.c

···
 	} else {
 		esp->min_period = ((5 * esp->ccycle) / 1000);
 	}
+	if (esp->rev == FAS236) {
+		/*
+		 * The AM53c974 chip returns the same ID as FAS236;
+		 * try to configure glitch eater.
+		 */
+		u8 config4 = ESP_CONFIG4_GE1;
+		esp_write8(config4, ESP_CFG4);
+		config4 = esp_read8(ESP_CFG4);
+		if (config4 & ESP_CONFIG4_GE1) {
+			esp->rev = PCSCSI;
+			esp_write8(esp->config4, ESP_CFG4);
+		}
+	}
 	esp->max_period = (esp->max_period + 3)>>2;
 	esp->min_period = (esp->min_period + 3)>>2;
 
···
 		/* fallthrough... */
 
 	case FAS236:
-		/* Fast 236 or HME */
+	case PCSCSI:
+		/* Fast 236, AM53c974 or HME */
 		esp_write8(esp->config2, ESP_CFG2);
 		if (esp->rev == FASHME) {
 			u8 cfg3 = esp->target[0].esp_config3;
···
 	"FAS100A",
 	"FAST",
 	"FASHME",
+	"AM53C974",
 };
 
 static struct scsi_transport_template *esp_transport_template;

drivers/scsi/esp_scsi.h

···
 #define ESP_CTEST	0x0aUL		/* wo  Chip test register      0x28  */
 #define ESP_CFG2	0x0bUL		/* rw  Second cfg register     0x2c  */
 #define ESP_CFG3	0x0cUL		/* rw  Third cfg register      0x30  */
+#define ESP_CFG4	0x0dUL		/* rw  Fourth cfg register     0x34  */
 #define ESP_TCHI	0x0eUL		/* rw  High bits transf count  0x38  */
 #define ESP_UID		ESP_TCHI	/* ro  Unique ID code          0x38  */
 #define FAS_RLO		ESP_TCHI	/* rw  HME extended counter    0x38  */
···
 #define ESP_CONFIG3_EWIDE     0x40     /* Enable Wide-SCSI     (hme)         */
 #define ESP_CONFIG3_IMS       0x80     /* ID msg chk'ng        (esp/fas236)  */
 #define ESP_CONFIG3_OBPUSH    0x80     /* Push odd-byte to dma (hme)         */
+
+/* ESP config register 4 read-write, found only on am53c974 chips */
+#define ESP_CONFIG4_RADE      0x04     /* Active negation */
+#define ESP_CONFIG4_RAE       0x08     /* Active negation on REQ and ACK */
+#define ESP_CONFIG4_PWD       0x20     /* Reduced power feature */
+#define ESP_CONFIG4_GE0       0x40     /* Glitch eater bit 0 */
+#define ESP_CONFIG4_GE1       0x80     /* Glitch eater bit 1 */
+
+#define ESP_CONFIG_GE_12NS    (0)
+#define ESP_CONFIG_GE_25NS    (ESP_CONFIG_GE1)
+#define ESP_CONFIG_GE_35NS    (ESP_CONFIG_GE0)
+#define ESP_CONFIG_GE_0NS     (ESP_CONFIG_GE0 | ESP_CONFIG_GE1)
 
 /* ESP command register read-write */
 /* Group 1 commands:  These may be sent at any point in time to the ESP
···
 	FAS100A    = 0x04,
 	FAST       = 0x05,
 	FASHME     = 0x06,
+	PCSCSI     = 0x07,  /* AM53c974 */
 };
 
 struct esp_cmd_entry {
···
 	u8			bursts;
 	u8			config1;
 	u8			config2;
+	u8			config4;
 
 	u8			scsi_id;
 	u32			scsi_id_mask;