s390/boot: move sclp early buffer from fixed address in asm to C

To make the decompressor relocatable, the early SCLP buffer with a fixed
address must be replaced with a relocatable C buffer of the according size
and alignment as required by SCLP.

Introduce a new function sclp_early_set_buffer() into the SCLP driver
which enables the decompressor to change the SCLP early buffer at any time.
This will be useful when the decompressor becomes fully relocatable and
might need to change the SCLP early buffer to one with an address < 2G
as required by SCLP because it was loaded at an address >= 2G.

Signed-off-by: Alexander Egorenkov <[e-mail]>
Acked-by: Heiko Carstens <[e-mail]>
Signed-off-by: Heiko Carstens <[e-mail]>

arch/s390/boot/boot.h

···
 void parse_boot_command_line(void);
 void verify_facilities(void);
 void print_missing_facilities(void);
+void sclp_early_setup_buffer(void);
 void print_pgm_check_info(void);
 unsigned long get_random_base(unsigned long safe_addr);
 void __printf(1, 2) decompressor_printk(const char *fmt, ...);

arch/s390/boot/compressed/vmlinux.lds.S

···
 #include <asm/vmlinux.lds.h>
 #include <asm/thread_info.h>
 #include <asm/page.h>
+#include <asm/sclp.h>
 
 OUTPUT_FORMAT("elf64-s390", "elf64-s390", "elf64-s390")
 OUTPUT_ARCH(s390:64-bit)
···
 		KEEP(*(.dma.ex_table))
 		_stop_dma_ex_table = .;
 	}
-	.dma.data : { *(.dma.data) }
+	.dma.data : {
+		*(.dma.data)
+	}
 	. = ALIGN(PAGE_SIZE);
 	_edma = .;
 

arch/s390/boot/head.S

···
 	spt	6f-.LPG0(%r13)
 	mvc	__LC_LAST_UPDATE_TIMER(8),6f-.LPG0(%r13)
 	larl	%r15,_stack_end-STACK_FRAME_OVERHEAD
+	brasl	%r14,sclp_early_setup_buffer
 	brasl	%r14,verify_facilities
 	brasl	%r14,startup_kernel
 SYM_CODE_END(startup_normal)
···
 	.byte	0
 	.org	PARMAREA+__PARMAREA_SIZE
 SYM_DATA_END(parmarea)
-
-	.org	EARLY_SCCB_OFFSET
-	.fill	EXT_SCCB_READ_SCP
 
 	.org	HEAD_END

arch/s390/boot/sclp_early_core.c

···
 // SPDX-License-Identifier: GPL-2.0
+#include "boot.h"
 #include "../../../drivers/s390/char/sclp_early_core.c"
+
+/* SCLP early buffer must stay page-aligned and below 2GB */
+static char __sclp_early_sccb[EXT_SCCB_READ_SCP] __aligned(PAGE_SIZE);
+
+void sclp_early_setup_buffer(void)
+{
+	sclp_early_set_buffer(&__sclp_early_sccb);
+}

arch/s390/include/asm/sclp.h

···
 	u8 data[0];	/* Subsequent Data passed verbatim to SCLP ET 24 */
 } __packed;
 
+void sclp_early_set_buffer(void *sccb);
 int sclp_early_read_info(void);
 int sclp_early_read_storage_info(void);
 int sclp_early_get_core_info(struct sclp_core_info *info);

arch/s390/include/asm/setup.h

···
 #define _ASM_S390_SETUP_H
 
 #include <linux/bits.h>
-#include <asm/sclp.h>
 #include <uapi/asm/setup.h>
 #include <linux/build_bug.h>
 
 #define EP_OFFSET		0x10008
 #define EP_STRING		"S390EP"
 #define PARMAREA		0x10400
-#define EARLY_SCCB_OFFSET	0x11000
-#define HEAD_END		(EARLY_SCCB_OFFSET + EXT_SCCB_READ_SCP)
+#define HEAD_END		0x11000
 
 /*
  * Machine features detected in early.c

drivers/s390/char/sclp_early_core.c

···
 
 static struct read_info_sccb __bootdata(sclp_info_sccb);
 static int __bootdata(sclp_info_sccb_valid);
-char *sclp_early_sccb = (char *) EARLY_SCCB_OFFSET;
+char *__bootdata(sclp_early_sccb);
 int sclp_init_state = sclp_init_state_uninitialized;
 /*
  * Used to keep track of the size of the event masks. Qemu until version 2.11
···
 	*have_linemode = sclp_early_con_check_linemode(sccb);
 	*have_vt220 = !!(sccb_get_send_mask(sccb) & EVTYP_VT220MSG_MASK);
 	return rc;
+}
+
+void sclp_early_set_buffer(void *sccb)
+{
+	sclp_early_sccb = sccb;
 }
 
 /*