ata: Prefer using "virtual" sector size where possible

Normally, if a device uses larger physical sector size than the logical
size and supports so-called "512e" mode, we let the device deal with
partial sector reads/writes.

However, if MAX_VIRT_SECTOR_SIZE is defined, we support
partitioning/filesystems that use a larger "virtual" sector than the
logical sector.  typically this matches the physical sector size of the
drive, which means that despite a small logical sector size, all I/O
is done in terms of the physical sector size.

Therefore, when MAX_VIRT_SECTOR_SIZE and MAX_PHYS_SECTOR_SIZE are
enabled (currently only ipod5g and ipod6g), prefer software-based
partial sector I/O.

Change-Id: I0815ad0a2f987b89bb2debfbf3d0ed64cdf85525

firmware/common/disk.c

@@ -434,6 +434,11 @@ int disk_mount(int drive)
             }
 #endif /* MAX_VIRT_SECTOR_SIZE */
         }
+
+#if defined(MAX_VIRT_SECTOR_SIZE) && defined(MAX_PHYS_SECTOR_SIZE)
+        if (mounted)
+            ata_set_phys_sector_mult(disk_sector_multiplier[drive]);
+#endif
     }
 
     disk_writer_unlock();

firmware/drivers/ata-common.c

@@ -238,6 +238,10 @@ static int ata_get_phys_sector_mult(void)
         /* Check if drive really needs emulation  - if we can access
            sector 1 then assume the drive supports "512e" and will handle
            it better than us, so ignore the large physical sectors.
+
+           The exception here is if the device is partitioned to use
+           larger-than-logical "virtual" sectors; in that case we will
+           use whichever one (ie physical/"virtual") is larger.
         */
         char throwaway[__MAX_VARIABLE_LOG_SECTOR];
         rc = ata_transfer_sectors(1, 1, &throwaway, false);
@@ -254,4 +258,15 @@ static int ata_get_phys_sector_mult(void)
     return 0;
 }
 
+void ata_set_phys_sector_mult(unsigned int mult)
+{
+    unsigned int max = MAX_PHYS_SECTOR_SIZE/log_sector_size;
+    /* virtual sector could be larger than pyhsical sector */
+    if (!mult || mult > max)
+        mult = max;
+    /* It needs to be at _least_ the size of the real multiplier */
+    if (mult > phys_sector_mult)
+        phys_sector_mult = mult;
+}
+
 #endif  /* MAX_PHYS_SECTOR_SIZE */

firmware/export/ata.h

@@ -235,4 +235,8 @@ int ata_read_smart(struct ata_smart_values*);
 
 #define ATA_IDENTIFY_WORDS 256
 
+#ifdef MAX_PHYS_SECTOR_SIZE
+void ata_set_phys_sector_mult(unsigned int mult);
+#endif
+
 #endif /* __ATA_H__ */