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[vesafb] Select an optimal mode, rather than the first acceptable mode
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There is no requirement for VBE modes to be listed in increasing order
of resolution.  With the present logic, this can cause e.g. a 1024x768
mode to be selected if the user asks for 640x480, if the 1024x768 mode
is earlier in the mode list.

Define a scoring system for modes as

  score = ( width * height - bpp )

and choose the mode with the lowest score among all acceptable modes.
This should prefer to choose the mode closest to the requested
resolution, with a slight preference for higher colour depths.

Reported-by: Robin Smidsrød <robin@smidsrod.no>
Signed-off-by: Michael Brown <mcb30@ipxe.org>
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@mcb30
mcb30 committed Nov 28, 2013
1 parent 00bb192 commit d4f7816
Showing 1 changed file with 91 additions and 49 deletions.
140 changes: 91 additions & 49 deletions src/arch/i386/interface/pcbios/vesafb.c
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Expand Up @@ -27,6 +27,7 @@ FILE_LICENCE ( GPL2_OR_LATER );

#include <stdlib.h>
#include <errno.h>
#include <limits.h>
#include <realmode.h>
#include <ipxe/console.h>
#include <ipxe/io.h>
Expand Down Expand Up @@ -211,27 +212,61 @@ static int vesafb_mode_list ( uint16_t **mode_numbers ) {
}

/**
* Set video mode
* Get video mode information
*
* @v mode_number Mode number
* @v mode Mode information
* @ret rc Return status code
*/
static int vesafb_set_mode ( unsigned int mode_number,
struct vbe_mode_info *mode ) {
static int vesafb_mode_info ( unsigned int mode_number ) {
struct vbe_mode_info *mode = &vbe_buf.mode;
uint16_t status;
int rc;

/* Select this mode */
/* Get mode information */
__asm__ __volatile__ ( REAL_CODE ( "int $0x10" )
: "=a" ( status )
: "a" ( VBE_SET_MODE ),
"b" ( mode_number ) );
: "a" ( VBE_MODE_INFO ),
"c" ( mode_number ),
"D" ( __from_data16 ( mode ) )
: "memory" );
if ( ( rc = vesafb_rc ( status ) ) != 0 ) {
DBGC ( &vbe_buf, "VESAFB could not set mode %04x: [%04x] %s\n",
mode_number, status, strerror ( rc ) );
DBGC ( &vbe_buf, "VESAFB could not get mode %04x information: "
"[%04x] %s\n", mode_number, status, strerror ( rc ) );
return rc;
}
DBGC ( &vbe_buf, "VESAFB mode %04x %dx%d %dbpp(%d:%d:%d:%d) model "
"%02x [x%d]%s%s%s%s%s\n", mode_number, mode->x_resolution,
mode->y_resolution, mode->bits_per_pixel, mode->rsvd_mask_size,
mode->red_mask_size, mode->green_mask_size, mode->blue_mask_size,
mode->memory_model, ( mode->number_of_image_pages + 1 ),
( ( mode->mode_attributes & VBE_MODE_ATTR_SUPPORTED ) ?
"" : " [unsupported]" ),
( ( mode->mode_attributes & VBE_MODE_ATTR_TTY ) ?
" [tty]" : "" ),
( ( mode->mode_attributes & VBE_MODE_ATTR_GRAPHICS ) ?
"" : " [text]" ),
( ( mode->mode_attributes & VBE_MODE_ATTR_LINEAR ) ?
"" : " [nonlinear]" ),
( ( mode->mode_attributes & VBE_MODE_ATTR_TRIPLE_BUF ) ?
" [buf]" : "" ) );

return 0;
}

/**
* Set video mode
*
* @v mode_number Mode number
* @ret rc Return status code
*/
static int vesafb_set_mode ( unsigned int mode_number ) {
struct vbe_mode_info *mode = &vbe_buf.mode;
uint16_t status;
int rc;

/* Get mode information */
if ( ( rc = vesafb_mode_info ( mode_number ) ) != 0 )
return rc;

/* Record mode parameters */
vesafb.start = mode->phys_base_ptr;
Expand All @@ -250,24 +285,37 @@ static int vesafb_set_mode ( unsigned int mode_number,
vesafb.map.green_lsb = mode->green_field_position;
vesafb.map.blue_lsb = mode->blue_field_position;

/* Select this mode */
__asm__ __volatile__ ( REAL_CODE ( "int $0x10" )
: "=a" ( status )
: "a" ( VBE_SET_MODE ),
"b" ( mode_number ) );
if ( ( rc = vesafb_rc ( status ) ) != 0 ) {
DBGC ( &vbe_buf, "VESAFB could not set mode %04x: [%04x] %s\n",
mode_number, status, strerror ( rc ) );
return rc;
}

return 0;
}

/**
* Select and set video mode
* Select video mode
*
* @v mode_numbers Mode number list (terminated with VBE_MODE_END)
* @v min_width Minimum required width (in pixels)
* @v min_height Minimum required height (in pixels)
* @v min_bpp Minimum required colour depth (in bits per pixel)
* @ret rc Return status code
* @ret mode_number Mode number, or negative error
*/
static int vesafb_select_mode ( const uint16_t *mode_numbers,
unsigned int min_width, unsigned int min_height,
unsigned int min_bpp ) {
struct vbe_mode_info *mode = &vbe_buf.mode;
int best_mode_number = -ENOENT;
unsigned int best_score = INT_MAX;
unsigned int score;
uint16_t mode_number;
uint16_t status;
int rc;

/* Find the first suitable mode */
Expand All @@ -277,35 +325,8 @@ static int vesafb_select_mode ( const uint16_t *mode_numbers,
mode_number |= VBE_MODE_LINEAR;

/* Get mode information */
__asm__ __volatile__ ( REAL_CODE ( "int $0x10" )
: "=a" ( status )
: "a" ( VBE_MODE_INFO ),
"c" ( mode_number ),
"D" ( __from_data16 ( mode ) )
: "memory" );
if ( ( rc = vesafb_rc ( status ) ) != 0 ) {
DBGC ( &vbe_buf, "VESAFB could not get mode %04x "
"information: [%04x] %s\n", mode_number,
status, strerror ( rc ) );
if ( ( rc = vesafb_mode_info ( mode_number ) ) != 0 )
continue;
}
DBGC ( &vbe_buf, "VESAFB mode %04x %dx%d %dbpp(%d:%d:%d:%d) "
"model %02x [x%d]%s%s%s%s%s\n", mode_number,
mode->x_resolution, mode->y_resolution,
mode->bits_per_pixel, mode->rsvd_mask_size,
mode->red_mask_size, mode->green_mask_size,
mode->blue_mask_size, mode->memory_model,
( mode->number_of_image_pages + 1 ),
( ( mode->mode_attributes & VBE_MODE_ATTR_SUPPORTED ) ?
"" : " [unsupported]" ),
( ( mode->mode_attributes & VBE_MODE_ATTR_TTY ) ?
" [tty]" : "" ),
( ( mode->mode_attributes & VBE_MODE_ATTR_GRAPHICS ) ?
"" : " [text]" ),
( ( mode->mode_attributes & VBE_MODE_ATTR_LINEAR ) ?
"" : " [nonlinear]" ),
( ( mode->mode_attributes & VBE_MODE_ATTR_TRIPLE_BUF ) ?
" [buf]" : "" ) );

/* Skip unusable modes */
if ( ( mode->mode_attributes & ( VBE_MODE_ATTR_SUPPORTED |
Expand All @@ -325,15 +346,28 @@ static int vesafb_select_mode ( const uint16_t *mode_numbers,
continue;
}

/* Select this mode */
if ( ( rc = vesafb_set_mode ( mode_number, mode ) ) != 0 )
return rc;
/* Select this mode if it has the best (i.e. lowest)
* score. We choose the scoring system to favour
* modes close to the specified width and height;
* within modes of the same width and height we prefer
* a higher colour depth.
*/
score = ( ( mode->x_resolution * mode->y_resolution ) -
mode->bits_per_pixel );
if ( score < best_score ) {
best_mode_number = mode_number;
best_score = score;
}
}

return 0;
if ( best_mode_number >= 0 ) {
DBGC ( &vbe_buf, "VESAFB selected mode %04x\n",
best_mode_number );
} else {
DBGC ( &vbe_buf, "VESAFB found no suitable mode\n" );
}

DBGC ( &vbe_buf, "VESAFB found no suitable mode\n" );
return -ENOENT;
return best_mode_number;
}

/**
Expand All @@ -349,6 +383,7 @@ static int vesafb_init ( unsigned int min_width, unsigned int min_height,
unsigned int min_bpp, struct pixel_buffer *pixbuf ) {
uint32_t discard_b;
uint16_t *mode_numbers;
int mode_number;
int rc;

/* Record current VGA mode */
Expand All @@ -361,10 +396,16 @@ static int vesafb_init ( unsigned int min_width, unsigned int min_height,
if ( ( rc = vesafb_mode_list ( &mode_numbers ) ) != 0 )
goto err_mode_list;

/* Select and set mode */
if ( ( rc = vesafb_select_mode ( mode_numbers, min_width, min_height,
min_bpp ) ) != 0 )
/* Select mode */
if ( ( mode_number = vesafb_select_mode ( mode_numbers, min_width,
min_height, min_bpp ) ) < 0 ){
rc = mode_number;
goto err_select_mode;
}

/* Set mode */
if ( ( rc = vesafb_set_mode ( mode_number ) ) != 0 )
goto err_set_mode;

/* Get font data */
vesafb_font();
Expand All @@ -373,6 +414,7 @@ static int vesafb_init ( unsigned int min_width, unsigned int min_height,
fbcon_init ( &vesafb.fbcon, phys_to_user ( vesafb.start ),
&vesafb.pixel, &vesafb.map, &vesafb.font, pixbuf );

err_set_mode:
err_select_mode:
free ( mode_numbers );
err_mode_list:
Expand Down

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