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From:   Naveen Naidu <naveennaidu479@gmail.com>
To:     bhelgaas@google.com
Cc:     Naveen Naidu <naveennaidu479@gmail.com>,
        linux-kernel-mentees@lists.linuxfoundation.org,
        linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
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Subject: [PATCH 01/22] PCI: Add PCI_ERROR_RESPONSE and it's related defintions
Date:   Mon, 11 Oct 2021 23:07:53 +0530
Message-Id: <5b4ba38fa56c7625d391383a3aed47dea6726946.1633972263.git.naveennaidu479@gmail.com>
In-Reply-To: <cover.1633972263.git.naveennaidu479@gmail.com>
References: <cover.1633972263.git.naveennaidu479@gmail.com>
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An MMIO read from a PCI device that doesn't exist or doesn't respond
causes a PCI error.  There's no real data to return to satisfy the
CPU read, so most hardware fabricates ~0 data.

Add a PCI_ERROR_RESPONSE definition for that and use it where
appropriate to make these checks consistent and easier to find.

Also add helper definitions SET_PCI_ERROR_RESPONSE and
RESPONSE_IS_PCI_ERROR to make the code more readable.

Signed-off-by: Naveen Naidu <naveennaidu479@gmail.com>
---
 include/linux/pci.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/include/linux/pci.h b/include/linux/pci.h
index cd8aa6fce204..928c589bb5c4 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -154,6 +154,15 @@ enum pci_interrupt_pin {
 /* The number of legacy PCI INTx interrupts */
 #define PCI_NUM_INTX	4
 
+/*
+ * Reading from a device that doesn't respond typically returns ~0.  A
+ * successful read from a device may also return ~0, so you need additional
+ * information to reliably identify errors.
+ */
+#define PCI_ERROR_RESPONSE			(~0ULL)
+#define SET_PCI_ERROR_RESPONSE(val)	(*val = ((typeof(*val)) PCI_ERROR_RESPONSE))
+#define RESPONSE_IS_PCI_ERROR(val)	(*val == ((typeof(*val)) PCI_ERROR_RESPONSE))
+
 /*
  * pci_power_t values must match the bits in the Capabilities PME_Support
  * and Control/Status PowerState fields in the Power Management capability.
-- 
2.25.1