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drm/ast: DisplayPort edid supports 256 bytes

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DisplayPort supports EDID up to 256 bytes (blocks 0 and 1). Update the
block check to allow these two blocks. For any block beyond that
(i.e. the monitor's EDID is larger than the 256 bytes ASPEED DP can
hold), report it as an all-zero block instead of a read failure.

Also remove the manual checksum/extension-count patch of block 0's
last four bytes. That code was already dead, so the condition can never
be true.

Signed-off-by: Jammy Huang <jammy_huang@aspeedtech.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patch.msgid.link/20260819-upstream_ast_dp_edid-v3-1-15d36c28afe2@aspeedtech.com
This commit is contained in:
Jammy Huang 2026-08-19 13:58:37 +08:00 committed by Thomas Zimmermann
parent 1ae7fe832c
commit b35be235d9
1 changed files with 8 additions and 16 deletions
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24
drivers/gpu/drm/ast/ast_dp.c
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@ -88,8 +88,14 @@ static int ast_astdp_read_edid_block(void *data, u8 *buf, unsigned int block, si
int ret = 0;
unsigned int i;
if (block > 0)
return -EIO; /* extension headers not supported */
if (block > 1) {
/* ASPEED DP's EDID buffer holds blocks 0 and 1 only (256
* bytes). Report anything beyond that as an all-zero block
* rather than a read failure.
*/
memset(buf, 0, len);
return 0;
}
/*
* Protect access to I/O registers from concurrent modesetting
@ -154,20 +160,6 @@ static int ast_astdp_read_edid_block(void *data, u8 *buf, unsigned int block, si
ediddata[2] = ast_get_index_reg(ast, AST_IO_VGACRI, 0xda);
ediddata[3] = ast_get_index_reg(ast, AST_IO_VGACRI, 0xdb);
if (i == 31) {
/*
* For 128-bytes EDID_1.3,
* 1. Add the value of Bytes-126 to Bytes-127.
* The Bytes-127 is Checksum. Sum of all 128bytes should
* equal 0 (mod 256).
* 2. Modify Bytes-126 to be 0.
* The Bytes-126 indicates the Number of extensions to
* follow. 0 represents noextensions.
*/
ediddata[3] = ediddata[3] + ediddata[2];
ediddata[2] = 0;
}
memcpy(buf, ediddata, min((len - i), 4));
buf += 4;
}