PCI/ATS: Use FIELD_GET()

Use FIELD_GET() to remove dependences on the field position, i.e., the
shift value.  No functional change intended.

Link: https://lore.kernel.org/r/20231010204436.1000644-6-helgaas@kernel.org
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

Author: bjorn-helgaas

drivers/pci/ats.c

@@ -9,6 +9,7 @@
  * Copyright (C) 2011 Advanced Micro Devices,
  */
 
+#include <linux/bitfield.h>
 #include <linux/export.h>
 #include <linux/pci-ats.h>
 #include <linux/pci.h>
@@ -480,8 +481,6 @@ int pci_pasid_features(struct pci_dev *pdev)
 }
 EXPORT_SYMBOL_GPL(pci_pasid_features);
 
-#define PASID_NUMBER_SHIFT	8
-#define PASID_NUMBER_MASK	(0x1f << PASID_NUMBER_SHIFT)
 /**
  * pci_max_pasids - Get maximum number of PASIDs supported by device
  * @pdev: PCI device structure
@@ -503,9 +502,7 @@ int pci_max_pasids(struct pci_dev *pdev)
 
 	pci_read_config_word(pdev, pasid + PCI_PASID_CAP, &supported);
 
-	supported = (supported & PASID_NUMBER_MASK) >> PASID_NUMBER_SHIFT;
-
-	return (1 << supported);
+	return (1 << FIELD_GET(PCI_PASID_CAP_WIDTH, supported));
 }
 EXPORT_SYMBOL_GPL(pci_max_pasids);
 #endif /* CONFIG_PCI_PASID */

include/uapi/linux/pci_regs.h

@@ -932,6 +932,7 @@
 #define PCI_PASID_CAP		0x04    /* PASID feature register */
 #define  PCI_PASID_CAP_EXEC	0x0002	/* Exec permissions Supported */
 #define  PCI_PASID_CAP_PRIV	0x0004	/* Privilege Mode Supported */
+#define  PCI_PASID_CAP_WIDTH	0x1f00
 #define PCI_PASID_CTRL		0x06    /* PASID control register */
 #define  PCI_PASID_CTRL_ENABLE	0x0001	/* Enable bit */
 #define  PCI_PASID_CTRL_EXEC	0x0002	/* Exec permissions Enable */