hw/char/parallel: Make it possible to compile also without CONFIG_PARALLEL

For the downstream distribution of QEMU, we want to compile without
CONFIG_PARALLEL. Commit 9157eee1b1c076ff3 already moved the function
parallel_hds_isa_init() (which is still required for linking) into a file
that is included anyway, but commit bb3d5ea858e7f888563a moved it
to a separate file which is only compiled again if CONFIG_PARALLEL is
set. To be able to link QEMU again without CONFIG_PARALLEL, the file
should be considered for linking for all targets that have CONFIG_ISA_BUS.
And while we're at it, add a proper comment in there with the rationale
for the separate file.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <1552297854-25847-1-git-send-email-thuth@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/char/Makefile.objs

@@ -2,7 +2,7 @@ common-obj-$(CONFIG_IPACK) += ipoctal232.o
 common-obj-$(CONFIG_ESCC) += escc.o
 common-obj-$(CONFIG_NRF51_SOC) += nrf51_uart.o
 common-obj-$(CONFIG_PARALLEL) += parallel.o
-common-obj-$(CONFIG_PARALLEL) += parallel-isa.o
+common-obj-$(CONFIG_ISA_BUS) += parallel-isa.o
 common-obj-$(CONFIG_PL011) += pl011.o
 common-obj-$(CONFIG_SERIAL) += serial.o
 common-obj-$(CONFIG_SERIAL_ISA) += serial-isa.o

hw/char/parallel-isa.c

@@ -1,6 +1,9 @@
 /*
  * QEMU Parallel PORT (ISA bus helpers)
  *
+ * These functions reside in a separate file since they also might be
+ * required for linking when compiling QEMU without CONFIG_PARALLEL.
+ *
  * Copyright (c) 2003 Fabrice Bellard
  *
  * SPDX-License-Identifier: MIT

hw/i386/Kconfig

@@ -9,6 +9,7 @@ config PC
     imply ISA_IPMI_KCS
     imply ISA_IPMI_BT
     imply ISA_DEBUG
+    imply PARALLEL
     imply PCI_DEVICES
     imply PVPANIC
     imply QXL
@@ -25,8 +26,6 @@ config PC
     select I82374
     select I8257
     select MC146818RTC
-    # Needed by the board code:
-    select PARALLEL
     # For ACPI builder:
     select SERIAL_ISA
     select ACPI_VMGENID

hw/sparc64/Kconfig

@@ -3,13 +3,13 @@ config SUN4U
     imply PCI_DEVICES
     imply SUNHME
     imply TEST_DEVICES
+    imply PARALLEL
     select M48T59
     select ISA_BUS
     select FDC
     select SERIAL_ISA
     select PCI_SABRE
     select IDE_CMD646
-    select PARALLEL
     select PCKBD
     select SIMBA