From 4a2aefc117144a87d5fc515ddcb60c7d13dcaf1e Mon Sep 17 00:00:00 2001
From: Anton Kling <anton@kling.gg>
Date: Sun, 30 Jun 2024 19:38:31 +0200
Subject: AHCI: Optimization to writes

Now it avoids waiting for completion if possible and can instead batch
commands.
---
 kernel/drivers/ahci.c | 65 +++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 47 insertions(+), 18 deletions(-)

(limited to 'kernel/drivers')

diff --git a/kernel/drivers/ahci.c b/kernel/drivers/ahci.c
index bef11ae..530295d 100644
--- a/kernel/drivers/ahci.c
+++ b/kernel/drivers/ahci.c
@@ -303,20 +303,33 @@ u8 get_free_command_slot(volatile struct HBA_PORT *port, u8 *err) {
   return 0;
 }
 
+void ahci_wait_for_completion(volatile struct HBA_PORT *port) {
+  u32 num_slots = ((hba->cap >> 8) & 0x1F);
+  u32 slots = (port->ci);
+  u32 num_free = 0;
+  for (; num_free < 10;) {
+    num_free = 0;
+    for (u8 i = 0; i < num_slots + 1; i++) {
+      if (!((slots >> i) & 1)) {
+        num_free++;
+      }
+    }
+  }
+}
+
 // is_write: Determins whether a read or write command will be used.
 u8 ahci_perform_command(volatile struct HBA_PORT *port, u32 startl, u32 starth,
-                        u32 count, u16 *buffer, u8 is_write) {
+                        u32 count, u16 *buffer, u8 is_write, u8 async) {
   // TODO: The number of PRDT tables are hardcoded at a seemingly
   // very low number. It can be up to 65,535. Should it maybe be
   // changed?
   assert(count <= num_prdt);
   port->is = -1; // Clear pending interrupts
   u8 err;
-  u32 command_slot = get_free_command_slot(port, &err);
-  if (err) {
-    klog(LOG_WARN, "AHCI No command slot found");
-    return 0;
-  }
+  u32 command_slot;
+  do {
+    command_slot = get_free_command_slot(port, &err);
+  } while (err);
   struct HBA_CMD_HEADER *cmdheader =
       (struct HBA_CMD_HEADER *)physical_to_virtual((void *)port->clb);
   assert(0x20 == sizeof(struct HBA_CMD_HEADER));
@@ -381,6 +394,10 @@ u8 ahci_perform_command(volatile struct HBA_PORT *port, u32 startl, u32 starth,
 
   port->ci = 1 << command_slot; // Issue command
 
+  if (async) {
+    return 1;
+  }
+
   // Wait for completion
   for (;;) {
     // In some longer duration reads, it may be helpful to spin on the DPS bit
@@ -404,13 +421,13 @@ u8 ahci_perform_command(volatile struct HBA_PORT *port, u32 startl, u32 starth,
 }
 
 u8 ahci_raw_write(volatile struct HBA_PORT *port, u32 startl, u32 starth,
-                  u32 count, u16 *inbuffer) {
-  return ahci_perform_command(port, startl, starth, count, inbuffer, 1);
+                  u32 count, u16 *inbuffer, u8 async) {
+  return ahci_perform_command(port, startl, starth, count, inbuffer, 1, async);
 }
 
 u8 ahci_raw_read(volatile struct HBA_PORT *port, u32 startl, u32 starth,
-                 u32 count, u16 *outbuffer) {
-  return ahci_perform_command(port, startl, starth, count, outbuffer, 0);
+                 u32 count, u16 *outbuffer, u8 async) {
+  return ahci_perform_command(port, startl, starth, count, outbuffer, 0, async);
 }
 
 int ahci_write(u8 *buffer, u64 offset, u64 len, vfs_fd_t *fd) {
@@ -428,13 +445,13 @@ int ahci_write(u8 *buffer, u64 offset, u64 len, vfs_fd_t *fd) {
 
   if (offset > 0) {
     u8 tmp_buffer[512];
-    ahci_raw_read(&hba->ports[port], lba, 0, 1, (u16 *)tmp_buffer);
+    ahci_raw_read(&hba->ports[port], lba, 0, 1, (u16 *)tmp_buffer, 0);
 
     int left = 512 - offset;
     int write = min(left, len);
 
     memcpy(tmp_buffer + offset, buffer, write);
-    ahci_raw_write(&hba->ports[port], lba, 0, 1, (u16 *)tmp_buffer);
+    ahci_raw_write(&hba->ports[port], lba, 0, 1, (u16 *)tmp_buffer, 0);
 
     offset = 0;
     len -= write;
@@ -443,17 +460,28 @@ int ahci_write(u8 *buffer, u64 offset, u64 len, vfs_fd_t *fd) {
   }
 
   for (; sector_count >= num_prdt; lba++) {
-    ahci_raw_write(&hba->ports[port], lba, 0, num_prdt, (u16 *)buffer);
+    ahci_raw_write(&hba->ports[port], lba, 0, num_prdt, (u16 *)buffer, 1);
     buffer += num_prdt * 512;
     len -= num_prdt * 512;
     sector_count -= num_prdt;
   }
 
+  if (sector_count >= num_prdt) {
+    ahci_wait_for_completion(&hba->ports[port]);
+  }
+
+  if (sector_count > 0 && (0 == len % SECTOR_SIZE)) {
+    ahci_raw_write(&hba->ports[port], lba, 0, sector_count, (u16 *)buffer, 0);
+    return rc;
+  }
+
   if (sector_count > 0 && len > 0) {
-    u8 tmp_buffer[512 * num_prdt];
-    ahci_raw_read(&hba->ports[port], lba, 0, sector_count, (u16 *)tmp_buffer);
+    u8 tmp_buffer[512 * sector_count];
+    ahci_raw_read(&hba->ports[port], lba, 0, sector_count, (u16 *)tmp_buffer,
+                  0);
     memcpy(tmp_buffer + offset, buffer, len);
-    ahci_raw_write(&hba->ports[port], lba, 0, sector_count, (u16 *)tmp_buffer);
+    ahci_raw_write(&hba->ports[port], lba, 0, sector_count, (u16 *)tmp_buffer,
+                   0);
   }
   return rc;
 }
@@ -472,7 +500,7 @@ int ahci_read(u8 *buffer, u64 offset, u64 len, vfs_fd_t *fd) {
   }
   u8 tmp_buffer[512 * num_prdt];
   for (; sector_count >= num_prdt; lba++) {
-    ahci_raw_read(&hba->ports[port], lba, 0, num_prdt, (u16 *)tmp_buffer);
+    ahci_raw_read(&hba->ports[port], lba, 0, num_prdt, (u16 *)tmp_buffer, 0);
     memcpy(buffer, tmp_buffer + offset, 512 * num_prdt);
     offset = 0;
     buffer += num_prdt * 512;
@@ -481,7 +509,8 @@ int ahci_read(u8 *buffer, u64 offset, u64 len, vfs_fd_t *fd) {
   }
 
   if (sector_count > 0) {
-    ahci_raw_read(&hba->ports[port], lba, 0, sector_count, (u16 *)tmp_buffer);
+    ahci_raw_read(&hba->ports[port], lba, 0, sector_count, (u16 *)tmp_buffer,
+                  0);
     memcpy(buffer, tmp_buffer + offset, len);
   }
   return rc;
-- 
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