On Tue, Feb 23, 2016 at 04:14:46PM +0200, Michael S. Tsirkin wrote:
On Tue, Feb 23, 2016 at 08:47:00AM -0500, Gabriel L. Somlo wrote:
quoted
On Tue, Feb 23, 2016 at 07:07:36AM +0200, Michael S. Tsirkin wrote:
quoted
On Mon, Feb 22, 2016 at 03:26:23PM -0500, Gabriel L. Somlo wrote:
quoted
On Mon, Feb 22, 2016 at 10:14:50PM +0200, Michael S. Tsirkin wrote:
quoted
On Sun, Feb 21, 2016 at 08:06:17AM -0500, Gabriel L. Somlo wrote:
quoted
quoted
quoted
+static void fw_cfg_io_cleanup(void)
+{
+ if (fw_cfg_is_mmio) {
+ iounmap(fw_cfg_dev_base);
+ release_mem_region(fw_cfg_p_base, fw_cfg_p_size);
+ } else {
+ ioport_unmap(fw_cfg_dev_base);
+ release_region(fw_cfg_p_base, fw_cfg_p_size);
+ }
+}
+
+/* arch-specific ctrl & data register offsets are not available in ACPI, DT */
So for all arches which support ACPI, I think this driver
should just rely on ACPI.
There was a discussion about that a few versions ago, and IIRC the
conclusion was not to expect the firmware to contend for fw_cfg access
after the guest kernel boots:
https://lkml.org/lkml/2015/10/5/283
So it looks like NVDIMM at least wants to pass label data to guest -
for which fw cfg might be a reasonable choice.
I suspect things changed - fw cfg used to be very slow but we now have
DMA interface which makes it useful for a range of applications.
Comment on this? I'm really worried we'll release linux
without a way to access fw cfg from aml.
How about taking acpi lock around all accesses?
You mean something like this (haven't tried compiling it yet, so it
might be a bit more complicated, but just for the purpose of this
conversation):
diff --git a/drivers/firmware/qemu_fw_cfg.c
b/drivers/firmware/qemu_fw_cfg.c
index fedbff5..3462a2c 100644
--- a/drivers/firmware/qemu_fw_cfg.c
+++ b/drivers/firmware/qemu_fw_cfg.c
@@ -77,12 +77,18 @@ static inline u16 fw_cfg_sel_endianness(u16 key)
static inline void fw_cfg_read_blob(u16 key,
void *buf, loff_t pos, size_tcount)
{
+#ifdef CONFIG_ACPI
+ acpi_os_acquire_mutex(acpi_gbl_osi_mutex, ACPI_WAIT_FOREVER);
+#endif
mutex_lock(&fw_cfg_dev_lock);
iowrite16(fw_cfg_sel_endianness(key), fw_cfg_reg_ctrl);
while (pos-- > 0)
ioread8(fw_cfg_reg_data);
ioread8_rep(fw_cfg_reg_data, buf, count);
mutex_unlock(&fw_cfg_dev_lock);
+#ifdef CONFIG_ACPI
+ acpi_os_release_mutex(acpi_gbl_osi_mutex);
+#endif
}
/* clean up fw_cfg device i/o */
Fundamentally yes.
quoted
I wouldn't particularly *mind* doing that, but I'd still like to hear
from other QEMU devs on whether it's really necessary.
It seems like a prudent thing to do IMHO, before this
goes out to users.
[...]
On balance, I think locking ACPI solves most problems so
if we just do that, I think what you did here is fine.
Only trouble is, acpi_gbl_osi_mutex seems to be "private" to the acpi
subsystem, and I'm not sure how well a patch to allow some random
module to lock/unlock ACPI at its convenience would be received...
So unless I'm missing something obvious (wouldn't be the first time),
I think we're back to where *if* we *have* to do this [*], providing an
AML blob-reader method in ACPI and punting to it from the guest-side
kernel module (via #ifdef CONFIG_ACPI) would be the less painful
alternative.
[*] that is, mutual exclusion between kernel and firmware regarding
fw_cfg is (back) on the table, for real this time...
It would be good to know that it's the new consensus among QEMU
folks, since I have a strong feeling I'd no longer be "Keeping It Simple"
by moving in this direction.
Thanks,
--Gabriel