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drm/ast: dp501: Fix initialization of SCU2C

Ast's DP501 initialization reads the register SCU2C at offset 0x1202c
and tries to set it to source data from VGA. But writes the update to
offset 0x0, with unknown results. Write the result to SCU instead.

The bug only happens in ast_init_analog(). There's similar code in
ast_init_dvo(), which works correctly.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: 83c6620bae3f ("drm/ast: initial DP501 support (v0.2)")
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Jocelyn Falempe <jfalempe@redhat.com>
Cc: dri-devel@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v3.16+
Link: https://patch.msgid.link/20260327133532.79696-2-tzimmermann@suse.de

Thomas Zimmermann 2f42c1a6 2feec5ae

+1 -1
+1 -1
drivers/gpu/drm/ast/ast_dp501.c
··· 436 436 /* Finally, clear bits [17:16] of SCU2c */ 437 437 data = ast_read32(ast, 0x1202c); 438 438 data &= 0xfffcffff; 439 - ast_write32(ast, 0, data); 439 + ast_write32(ast, 0x1202c, data); 440 440 441 441 /* Disable DVO */ 442 442 ast_set_index_reg_mask(ast, AST_IO_VGACRI, 0xa3, 0xcf, 0x00);