Jonathan Cameron <jonathan.came...@huawei.com> writes:
> On Wed, 26 Jan 2022 18:17:12 +0000
> Alex Bennée <alex.ben...@linaro.org> wrote:
>
>> Jonathan Cameron <jonathan.came...@huawei.com> writes:
>>
>> > From: Ben Widawsky <ben.widaw...@intel.com>
>> >
>> > This implements all device MMIO up to the first capability. That
>> > includes the CXL Device Capabilities Array Register, as well as all of
>> > the CXL Device Capability Header Registers. The latter are filled in as
>> > they are implemented in the following patches.
>> >
>> > Endianness and alignment are managed by softmmu memory core.
>> >
>> > Signed-off-by: Ben Widawsky <ben.widaw...@intel.com>
>> > Signed-off-by: Jonathan Cameron <jonathan.came...@huawei.com>
>> > ---
>> > hw/cxl/cxl-device-utils.c | 105 ++++++++++++++++++++++++++++++++++++
>> > hw/cxl/meson.build | 1 +
>> > include/hw/cxl/cxl_device.h | 28 +++++++++-
>> > 3 files changed, 133 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/hw/cxl/cxl-device-utils.c b/hw/cxl/cxl-device-utils.c
>> > new file mode 100644
>> > index 0000000000..cb1b0a8217
>> > --- /dev/null
>> > +++ b/hw/cxl/cxl-device-utils.c
>> > @@ -0,0 +1,105 @@
>> > +/*
>> > + * CXL Utility library for devices
>> > + *
>> > + * Copyright(C) 2020 Intel Corporation.
>> > + *
>> > + * This work is licensed under the terms of the GNU GPL, version 2. See
>> > the
>> > + * COPYING file in the top-level directory.
>> > + */
>> > +
>> > +#include "qemu/osdep.h"
>> > +#include "qemu/log.h"
>> > +#include "hw/cxl/cxl.h"
>> > +
>> > +/*
>> > + * Device registers have no restrictions per the spec, and so fall back
>> > to the
>> > + * default memory mapped register rules in 8.2:
>> > + * Software shall use CXL.io Memory Read and Write to access memory
>> > mapped
>> > + * register defined in this section. Unless otherwise specified,
>> > software
>> > + * shall restrict the accesses width based on the following:
>> > + * • A 32 bit register shall be accessed as a 1 Byte, 2 Bytes or 4 Bytes
>> > + * quantity.
>> > + * • A 64 bit register shall be accessed as a 1 Byte, 2 Bytes, 4 Bytes
>> > or 8
>> > + * Bytes
>> > + * • The address shall be a multiple of the access width, e.g. when
>> > + * accessing a register as a 4 Byte quantity, the address shall be
>> > + * multiple of 4.
>> > + * • The accesses shall map to contiguous bytes.If these rules are not
>> > + * followed, the behavior is undefined
>> > + */
>> > +
>> > +static uint64_t caps_reg_read(void *opaque, hwaddr offset, unsigned size)
>> > +{
>> > + CXLDeviceState *cxl_dstate = opaque;
>> > +
>> > + return cxl_dstate->caps_reg_state32[offset / 4];
>> > +}
>> > +
>> > +static uint64_t dev_reg_read(void *opaque, hwaddr offset, unsigned size)
>> > +{
>> > + return 0;
>> > +}
>> > +
>> > +static const MemoryRegionOps dev_ops = {
>> > + .read = dev_reg_read,
>> > + .write = NULL, /* status register is read only */
>> > + .endianness = DEVICE_LITTLE_ENDIAN,
>> > + .valid = {
>> > + .min_access_size = 1,
>> > + .max_access_size = 8,
>> > + .unaligned = false,
>> > + },
>> > + .impl = {
>> > + .min_access_size = 1,
>> > + .max_access_size = 8,
>> > + },
>> > +};
>>
>> I think for >64 bit registers you need to use the read_with_attrs
>
> I don't follow this comment. Max access to registers is 64 bits.
> A few are documented as 128 bit or indeed larger in the spec, but the
> access is as if they were multiple 64 bit registers accesses.
> It's not permissible to do a single 128bit access for example.
No that was my brain fart - of course 8 bytes = 64 bit which is fine for
the current accesses functions (unless you want bus faults).
>
> The F4 errata clarified that - previously it was rather unclear what
> the restrictions on access to the larger registers were.
>
> I've updated a few comments on this to reflect the errata.
>
> Thanks,
>
> Jonathan
--
Alex Bennée
