From b35be235d92b2826e1111bff4c85e080ffd8ca28 Mon Sep 17 00:00:00 2001 From: Jammy Huang Date: Wed, 19 Aug 2026 13:58:37 +0800 Subject: [PATCH] drm/ast: DisplayPort edid supports 256 bytes 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 Reviewed-by: Thomas Zimmermann Signed-off-by: Thomas Zimmermann Link: https://patch.msgid.link/20260819-upstream_ast_dp_edid-v3-1-15d36c28afe2@aspeedtech.com --- drivers/gpu/drm/ast/ast_dp.c | 24 ++++++++---------------- 1 file changed, 8 insertions(+), 16 deletions(-) diff --git a/drivers/gpu/drm/ast/ast_dp.c b/drivers/gpu/drm/ast/ast_dp.c index 5f266a05419b..f22c0c215a21 100644 --- a/drivers/gpu/drm/ast/ast_dp.c +++ b/drivers/gpu/drm/ast/ast_dp.c @@ -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; }