kern: pci: Handle base address registers (BARs)

This commit handles base address registers by storing them in a bar
array within the PCI device structure. We also introduced a helper
header to perform operations with BARs such as getting the length of
their underlying region

Signed-off-by: Ian Moffett <ian@osmora.org>

1 files changed, 67 insertions, 0 deletions

diff --git a/src/sys/arch/amd64/io/pci/bar.c b/src/sys/arch/amd64/io/pci/bar.c
new file mode 100644
index 0000000..d3cfd0b
--- /dev/null
+++ b/src/sys/arch/amd64/io/pci/bar.c
@@ -0,0 +1,67 @@
+/*
+ * Copyright (c) 2025 Ian Marco Moffett and L5 engineers
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the project nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/*
+ * Description: PCI base address register helpers
+ * Author: Ian Marco Moffett
+ */
+
+#include <sys/types.h>
+#include <sys/errno.h>
+#include <sys/panic.h>
+#include <io/pci/bar.h>
+
+/*
+ * Get the size of a BAR
+ */
+ssize_t
+pci_bar_size(struct pci_device *dev, uint8_t bar)
+{
+    uint32_t reg_tmp, reg;
+    uint8_t barreg = pci_get_barreg(bar);
+
+    if (dev == NULL) {
+        return -EINVAL;
+    }
+
+    /*
+     * A trick we can do to find the length of the BAR defined
+     * by the device is to see how many bits it is capable of
+     * decoding for a BAR then invert the mask as log2(length)
+     * bits must be unset.
+     */
+    reg_tmp = pci_readl(dev, barreg);
+    pci_writel(dev, barreg, 0xFFFFFFFF);
+    reg = pci_readl(dev, barreg);
+    reg = ~reg + 1;
+
+    /* Restore and return the length */
+    pci_writel(dev, barreg, reg_tmp);
+    return reg;
+}