auxdisplay: charlcd: Add support for 4-bit interfaces

In 4-bit mode, 8-bit commands and data are written using two raw writes
to the data interface: high nibble first, low nibble last.  This must be
handled by the low-level driver.

However, as we don't know in which mode (4-bit or 8-bit) nor 4-bit phase
the LCD was left, initialization must always be handled using raw
writes, and needs to configure the LCD for 8-bit mode first.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

2 files changed, 32 insertions, 6 deletions

diff --git a/drivers/auxdisplay/charlcd.c b/drivers/auxdisplay/charlcd.c
index 930ffb2fb317..b3a84e90a268 100644
--- a/drivers/auxdisplay/charlcd.c
+++ b/drivers/auxdisplay/charlcd.c
@@ -223,24 +223,46 @@ static void charlcd_clear_display(struct charlcd *lcd)
 
 static int charlcd_init_display(struct charlcd *lcd)
 {
+        void (*write_cmd_raw)(struct charlcd *lcd, int cmd);
         struct charlcd_priv *priv = to_priv(lcd);
+        u8 init;
+
+        if (lcd->ifwidth != 4 && lcd->ifwidth != 8)
+                return -EINVAL;
 
         priv->flags = ((lcd->height > 1) ? LCD_FLAG_N : 0) | LCD_FLAG_D |
                       LCD_FLAG_C | LCD_FLAG_B;
 
         long_sleep(20);         /* wait 20 ms after power-up for the paranoid */
 
-        /* 8bits, 1 line, small fonts; let's do it 3 times */
-        lcd->ops->write_cmd(lcd, LCD_CMD_FUNCTION_SET | LCD_CMD_DATA_LEN_8BITS);
+        /*
+         * 8-bit mode, 1 line, small fonts; let's do it 3 times, to make sure
+         * the LCD is in 8-bit mode afterwards
+         */
+        init = LCD_CMD_FUNCTION_SET | LCD_CMD_DATA_LEN_8BITS;
+        if (lcd->ifwidth == 4) {
+                init >>= 4;
+                write_cmd_raw = lcd->ops->write_cmd_raw4;
+        } else {
+                write_cmd_raw = lcd->ops->write_cmd;
+        }
+        write_cmd_raw(lcd, init);
         long_sleep(10);
-        lcd->ops->write_cmd(lcd, LCD_CMD_FUNCTION_SET | LCD_CMD_DATA_LEN_8BITS);
+        write_cmd_raw(lcd, init);
         long_sleep(10);
-        lcd->ops->write_cmd(lcd, LCD_CMD_FUNCTION_SET | LCD_CMD_DATA_LEN_8BITS);
+        write_cmd_raw(lcd, init);
         long_sleep(10);
 
+        if (lcd->ifwidth == 4) {
+                /* Switch to 4-bit mode, 1 line, small fonts */
+                lcd->ops->write_cmd_raw4(lcd, LCD_CMD_FUNCTION_SET >> 4);
+                long_sleep(10);
+        }
+
         /* set font height and lines number */
         lcd->ops->write_cmd(lcd,
-                LCD_CMD_FUNCTION_SET | LCD_CMD_DATA_LEN_8BITS |
+                LCD_CMD_FUNCTION_SET |
+                ((lcd->ifwidth == 8) ? LCD_CMD_DATA_LEN_8BITS : 0) |
                 ((priv->flags & LCD_FLAG_F) ? LCD_CMD_FONT_5X10_DOTS : 0) |
                 ((priv->flags & LCD_FLAG_N) ? LCD_CMD_TWO_LINES : 0));
         long_sleep(10);
@@ -482,7 +504,8 @@ static inline int handle_lcd_special_code(struct charlcd *lcd)
         /* check whether one of F,N flags was changed */
         else if ((oldflags ^ priv->flags) & (LCD_FLAG_F | LCD_FLAG_N))
                 lcd->ops->write_cmd(lcd,
-                        LCD_CMD_FUNCTION_SET | LCD_CMD_DATA_LEN_8BITS |
+                        LCD_CMD_FUNCTION_SET |
+                        ((lcd->ifwidth == 8) ? LCD_CMD_DATA_LEN_8BITS : 0) |
                         ((priv->flags & LCD_FLAG_F) ? LCD_CMD_FONT_5X10_DOTS : 0) |
                         ((priv->flags & LCD_FLAG_N) ? LCD_CMD_TWO_LINES : 0));
         /* check whether L flag was changed */
@@ -716,6 +739,7 @@ struct charlcd *charlcd_alloc(unsigned int drvdata_size)
         priv->esc_seq.len = -1;
 
         lcd = &priv->lcd;
+        lcd->ifwidth = 8;
         lcd->bwidth = DEFAULT_LCD_BWIDTH;
         lcd->hwidth = DEFAULT_LCD_HWIDTH;
         lcd->drvdata = priv->drvdata;
diff --git a/include/misc/charlcd.h b/include/misc/charlcd.h
index c40047b673c9..23f61850f363 100644
--- a/include/misc/charlcd.h
+++ b/include/misc/charlcd.h
@@ -14,6 +14,7 @@ struct charlcd {
         const struct charlcd_ops *ops;
         const unsigned char *char_conv; /* Optional */
 
+        int ifwidth;                    /* 4-bit or 8-bit (default) */
         int height;
         int width;
         int bwidth;                     /* Default set by charlcd_alloc() */
@@ -28,6 +29,7 @@ struct charlcd_ops {
         void (*write_data)(struct charlcd *lcd, int data);
 
         /* Optional */
+        void (*write_cmd_raw4)(struct charlcd *lcd, int cmd);   /* 4-bit only */
         void (*clear_fast)(struct charlcd *lcd);
         void (*backlight)(struct charlcd *lcd, int on);
 };