On 10/07/2021 18:49, Philippe Mathieu-Daudé wrote:
From: Mark Cave-Ayland <mark.cave-ayl...@ilande.co.uk>
Commit 3fe9a838ec "dp8393x: Always use 32-bit accesses" set
.impl.min_access_size
and .impl.max_access_size to 4 to try and fix the Linux jazzsonic driver which
uses
32-bit accesses.
The problem with forcing the register access to 32-bit in this way is that
since the
dp8393x uses 16-bit registers, a manual endian swap is required for devices on
big
endian machines with 32-bit accesses.
For both access sizes and machine endians the QEMU memory API can do the right
thing
automatically: all that is needed is to set .impl.min_access_size to 2 to
declare that
the dp8393x implements 16-bit registers.
Normally .impl.max_access_size should also be set to 2, however that doesn't
quite
work in this case since the register stride is specified using a (dynamic)
it_shift
property which is applied during the MMIO access itself. The effect of this is
that
for a 32-bit access the memory API performs 2 x 16-bit accesses, but the use of
it_shift within the MMIO access itself causes the register value to be repeated
in both
the top 16-bits and bottom 16-bits. The Linux jazzsonic driver expects the
stride to be
zero-extended up to access size and therefore fails to correctly detect the
dp8393x
device due to the extra data in the top 16-bits.
The solution here is to remove .impl.max_access_size so that the memory API will
correctly zero-extend the 16-bit registers to the access size up to and
including
it_shift. Since it_shift is never greater than 2 than this will always do the
right
thing for both 16-bit and 32-bit accesses regardless of the machine endian,
allowing
the manual endian swap code to be removed.
Signed-off-by: Mark Cave-Ayland <mark.cave-ayl...@ilande.co.uk>
Fixes: 3fe9a838ec ("dp8393x: Always use 32-bit accesses")
Message-Id: <20210705214929.17222-2-mark.cave-ayl...@ilande.co.uk>
Signed-off-by: Philippe Mathieu-Daudé <f4...@amsat.org>
---
hw/net/dp8393x.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)
diff --git a/hw/net/dp8393x.c b/hw/net/dp8393x.c
index a9224a5bc88..71c82a07c23 100644
--- a/hw/net/dp8393x.c
+++ b/hw/net/dp8393x.c
@@ -588,15 +588,14 @@ static uint64_t dp8393x_read(void *opaque, hwaddr addr,
unsigned int size)
trace_dp8393x_read(reg, reg_names[reg], val, size);
- return s->big_endian ? val << 16 : val;
+ return val;
}
-static void dp8393x_write(void *opaque, hwaddr addr, uint64_t data,
+static void dp8393x_write(void *opaque, hwaddr addr, uint64_t val,
unsigned int size)
{
dp8393xState *s = opaque;
int reg = addr >> s->it_shift;
- uint32_t val = s->big_endian ? data >> 16 : data;
trace_dp8393x_write(reg, reg_names[reg], val, size);
@@ -677,11 +676,16 @@ static void dp8393x_write(void *opaque, hwaddr addr, uint64_t data,
}
}
+/*
+ * Since .impl.max_access_size is effectively controlled by the it_shift
+ * property, leave it unspecified for now to allow the memory API to
+ * correctly zero extend the 16-bit register values to the access size up to
and
+ * including it_shift.
+ */
static const MemoryRegionOps dp8393x_ops = {
.read = dp8393x_read,
.write = dp8393x_write,
- .impl.min_access_size = 4,
- .impl.max_access_size = 4,
+ .impl.min_access_size = 2,
.endianness = DEVICE_NATIVE_ENDIAN,
};
Why has this been demoted to NOTFORMERGE? Removing the explicit .impl.max_access_size
= 4 means that we fall back to the default .impl.max_access_size = 4 which already
has a T-b tag from Finn for the series at
https://lists.gnu.org/archive/html/qemu-devel/2021-06/msg07167.html which includes
https://lists.gnu.org/archive/html/qemu-devel/2021-06/msg06814.html.
This patch with the explicit .impl.max_access_size = 4 was the primary motivation for
posting the original series nearly a month ago: see the original version at
https://lists.gnu.org/archive/html/qemu-devel/2021-06/msg03199.html.
ATB,
Mark.
