[PATCH] firewire: Add dummy read_csr/write_csr functions

[Hector Martin <marcan@marcan.st>]

This fixes segfaults when a card gets yanked off of the PCIe bus while
busy, e.g. with a userspace app trying to get the cycle time:

[8638860.994310] Call Trace:
[8638860.994313]  ioctl_get_cycle_timer2+0x4f/0xd0 [firewire_core]
[8638860.994323]  fw_device_op_ioctl+0xae/0x150 [firewire_core]
[8638860.994328]  __x64_sys_ioctl+0x7d/0xb0
[8638860.994332]  do_syscall_64+0x45/0x80
[8638860.994337]  entry_SYSCALL_64_after_hwframe+0x44/0xae

Signed-off-by: Hector Martin <marcan@marcan.st>
---
 drivers/firewire/core-card.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/firewire/core-card.c b/drivers/firewire/core-card.c
index 54be88167c60..d994da6cf465 100644
--- a/drivers/firewire/core-card.c
+++ b/drivers/firewire/core-card.c
@@ -616,6 +616,15 @@ static struct fw_iso_context *dummy_allocate_iso_context(struct fw_card *card,
 	return ERR_PTR(-ENODEV);
 }
 
+static u32 dummy_read_csr(struct fw_card *card, int csr_offset)
+{
+	return 0;
+}
+
+static void dummy_write_csr(struct fw_card *card, int csr_offset, u32 value)
+{
+}
+
 static int dummy_start_iso(struct fw_iso_context *ctx,
 			   s32 cycle, u32 sync, u32 tags)
 {
@@ -649,6 +658,8 @@ static const struct fw_card_driver dummy_driver_template = {
 	.send_response		= dummy_send_response,
 	.cancel_packet		= dummy_cancel_packet,
 	.enable_phys_dma	= dummy_enable_phys_dma,
+	.read_csr		= dummy_read_csr,
+	.write_csr		= dummy_write_csr,
 	.allocate_iso_context	= dummy_allocate_iso_context,
 	.start_iso		= dummy_start_iso,
 	.set_iso_channels	= dummy_set_iso_channels,
-- 
2.33.0