FAT: Add an option to force all transfers to be performed indirectly through the FAT file system's internal sector buffers

ChangeLog

@@ -11515,4 +11515,12 @@
 	* sched/pthread:  Add pthread_setaffinity() and pthread_getaffinity()
 	  (2016-02-19).
 	* sched/sched: Add sched_setaffinity() and sched_getaffinity() (2016-02-19).
+	* drivers/leds/rgbled.c: Add a driver to manage a RGB LED via PWM.  From
+	  Alan Carvalho de Assis (2016-02-22).
+	* arch/arm/src/stm32fcdiscovery: Add PWM support for the onboard RGB LED
+	  From Alan Carvalho de Assis (2016-02-22).
+	* arch/arm/src/samv7: HSMCI driver can now be configured to handle unaligned
+	  data buffers (2016-02-22).
+	* fs/fat:  Add an option to force all transfers to be performed indirectly
+	  using the FAT file system's internal sector buffers (2016-02-22).
 

fs/fat/Kconfig

@@ -13,6 +13,7 @@ config FS_FAT
 		Enable FAT filesystem support
 
 if FS_FAT
+
 config FAT_LCNAMES
 	bool "FAT upper/lower names"
 	default n
@@ -49,6 +50,29 @@ config FS_FATTIME
 		much sense in supporting FAT date and time unless you have a
 		hardware RTC or other way to get the time and date.
 
+config FAT_FORCE_INDIRECT
+bool "Force all in-direct transfers"
+default n
+---help---
+		Normally, the default behavior for the FAT file system is to perform
+		data transfers indirectly though specially allocated sector buffers
+		or, under certain circumstances, directly through user provided
+		buffers .  These circumstances are:  (1) The transfer is being
+		performed from the beginning of a sector (2) the user-provided
+		buffer will hold the full sector of data.
+
+		Some hardware, however, may require special DMA-capable memory or
+		specially aligned memory in order to perform the transfers.  In this
+		case, there may be no circumstance where the user buffer can be used.
+		Selecting this option will disable all attempts to use the user-
+		provided buffer:  All transfers will be force to be performed
+		indirectly through the FAT file systems sector buffers.
+
+		Note: This will have the negative impact of:  (1) An extra data
+		copy to transfer the data between the user buffer and the FAT file
+		systems internal sector buffers, and (2) A loss of performance
+		because I/O will be limited to one sector at a time.
+
 config FAT_DMAMEMORY
 	bool "DMA memory allocator"
 	default n
@@ -66,4 +90,4 @@ config FAT_DMAMEMORY
 		corresponding function that will be called to free the DMA-capable
 		memory.
 
-endif
+endif # FAT

fs/fat/fs_fat32.c

@@ -479,13 +479,16 @@ static ssize_t fat_read(FAR struct file *filep, FAR char *buffer,
   FAR struct fat_file_s *ff;
   unsigned int bytesread;
   unsigned int readsize;
-  unsigned int nsectors;
   size_t bytesleft;
   int32_t cluster;
   FAR uint8_t *userbuffer = (FAR uint8_t *)buffer;
   int sectorindex;
   int ret;
+
+#ifndef CONFIG_FAT_FORCE_INDIRECT
+  unsigned int nsectors;
   bool force_indirect = false;
+#endif
 
   /* Sanity checks */
 
@@ -590,6 +593,7 @@ static ssize_t fat_read(FAR struct file *filep, FAR char *buffer,
 fat_read_restart:
 #endif
 
+#ifndef CONFIG_FAT_FORCE_INDIRECT
       /* Check if the user has provided a buffer large enough to hold one
        * or more complete sectors -AND- the read is aligned to a sector
        * boundary.
@@ -636,7 +640,7 @@ fat_read_restart:
                   force_indirect = true;
                   goto fat_read_restart;
                 }
-#endif
+#endif /* CONFIG_FAT_DMAMEMORY */
 
               goto errout_with_semaphore;
             }
@@ -646,6 +650,7 @@ fat_read_restart:
           bytesread                = nsectors * fs->fs_hwsectorsize;
         }
       else
+#endif /* CONFIG_FAT_FORCE_INDIRECT */
         {
           /* We are reading a partial sector, or handling a non-DMA-able
            * whole-sector transfer.  First, read the whole sector
@@ -709,11 +714,14 @@ static ssize_t fat_write(FAR struct file *filep, FAR const char *buffer,
   int32_t cluster;
   unsigned int byteswritten;
   unsigned int writesize;
-  unsigned int nsectors;
   FAR uint8_t *userbuffer = (FAR uint8_t *)buffer;
   int sectorindex;
   int ret;
+
+#ifndef CONFIG_FAT_FORCE_INDIRECT
+  unsigned int nsectors;
   bool force_indirect = false;
+#endif
 
   /* Sanity checks.  I have seen the following assertion misfire if
    * CONFIG_DEBUG_MM is enabled while re-directing output to a
@@ -844,6 +852,7 @@ static ssize_t fat_write(FAR struct file *filep, FAR const char *buffer,
 fat_write_restart:
 #endif
 
+#ifndef CONFIG_FAT_FORCE_INDIRECT
       /* Check if the user has provided a buffer large enough to
        * hold one or more complete sectors.
        */
@@ -890,7 +899,7 @@ fat_write_restart:
                   force_indirect = true;
                   goto fat_write_restart;
                 }
-#endif
+#endif /* CONFIG_FAT_DMAMEMORY */
 
               goto errout_with_semaphore;
             }
@@ -901,6 +910,7 @@ fat_write_restart:
           ff->ff_bflags           |= FFBUFF_MODIFIED;
         }
       else
+#endif /* CONFIG_FAT_FORCE_INDIRECT */
         {
           /* Decide whether we are performing a read-modify-write
            * operation, in which case we have to read the existing sector