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    SubjectRe: [RFC PATCH v3 13/16] cxl/mem: Create concept of enabled commands
    On Thu, 21 Jan 2021 10:40:41 -0800
    Ben Widawsky <ben.widawsky@intel.com> wrote:

    > On 21-01-14 17:25:31, Jonathan Cameron wrote:
    > > On Mon, 11 Jan 2021 14:51:18 -0800
    > > Ben Widawsky <ben.widawsky@intel.com> wrote:
    > >
    > > > CXL devices must implement the Device Command Interface (described in
    > > > 8.2.9 of the CXL 2.0 spec). While the driver already maintains a list of
    > > > commands it supports, there is still a need to be able to distinguish
    > > > between commands that the driver knows about from commands that may not
    > > > be supported by the hardware. No such commands currently are defined in
    > > > the driver.
    > > >
    > > > The implementation leaves the statically defined table of commands and
    > > > supplements it with a bitmap to determine commands that are enabled.
    > > >
    > > > ---
    > > >
    > > > There are multiple approaches that can be taken, but this is nice for a
    > > > few reasons.
    > > >
    > > > Here are some of the other solutions:
    > > >
    > > > Create a per instance table with only the supported commands.
    > > > 1. Having a fixed command id -> command mapping is much easier to manage
    > > > for development and debugging.
    > > > 2. Dealing with dynamic memory allocation for the table adds unnecessary
    > > > complexity.
    > > > 3. Most tables for device types are likely to be quite similar.
    > > > 4. Makes it difficult to implement helper macros like cxl_for_each_cmd()
    > > >
    > > > If the per instance table did preserve ids, #1 above can be addressed.
    > > > However, as "enable" is currently the only mutable state for the
    > > > commands, it would yield a lot of overhead for not much gain.
    > > > Additionally, the other issues remain.
    > > >
    > > > If "enable" remains the only mutable state, I believe this to be the
    > > > best solution. Once the number of mutable elements in a command grows,
    > > > it probably makes sense to move to per device instance state with a
    > > > fixed command ID mapping.
    > > Agreed with the logic.
    > >
    > > However, patch wise, should either drop the --- above or move this below the
    > > --- after your sign off. Otherwise you run the risk of git dropping your
    > > sign off and resulting complaints from anyone run validation scripts
    > > of the kernel tree that check for that.
    > >
    > > >
    > > > Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
    > > > ---
    > > > drivers/cxl/cxl.h | 4 ++++
    > > > drivers/cxl/mem.c | 38 +++++++++++++++++++++++++++++++++++++-
    > > > 2 files changed, 41 insertions(+), 1 deletion(-)
    > > >
    > > > diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
    > > > index 537ac4d8e6bd..963ba30cb200 100644
    > > > --- a/drivers/cxl/cxl.h
    > > > +++ b/drivers/cxl/cxl.h
    > > > @@ -17,6 +17,9 @@
    > > >
    > > > #define CXL_GET_FIELD(word, field) FIELD_GET(field##_MASK, word)
    > > >
    > > > +/* XXX: Arbitrary max */
    > > > +#define CXL_MAX_COMMANDS 32
    > >
    > > If going this way, probably want a build time check that you don't
    > > go beyond this value for a given command set. I haven't actually
    > > thought about how to construct that but should be easy enough.
    > >
    >
    > I think BUILD_BUG_ON of ARRAY_SIZE mem_commands is sufficient. Let me know if
    > you want anything more.

    That is fine.

    >
    > > > +
    > > > /* Device (CXL 2.0 - 8.2.8.3) */
    > > > #define CXLDEV_CAP_ARRAY_REG 0x0
    > > > #define CXLDEV_CAP_ARRAY_CAP_ID 0
    > > > @@ -88,6 +91,7 @@ struct cxl_mem {
    > > > } ram;
    > > >
    > > > char firmware_version[0x10];
    > > > + DECLARE_BITMAP(enabled_cmds, CXL_MAX_COMMANDS);
    > > >
    > > > /* Cap 0001h - CXL_CAP_CAP_ID_DEVICE_STATUS */
    > > > struct {
    > > > diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
    > > > index a824cfd4342a..20b26fa2c466 100644
    > > > --- a/drivers/cxl/mem.c
    > > > +++ b/drivers/cxl/mem.c
    > > > @@ -114,6 +114,8 @@ static struct {
    > > > * would typically be used for deprecated commands.
    > > > * * %CXL_CMD_FLAG_MANDATORY: Hardware must support this command. This flag is
    > > > * only used internally by the driver for sanity checking.
    > > > + * * %CXL_CMD_INTERNAL_FLAG_PSEUDO: This is a pseudo command which doesn't have
    > > > + * a direct mapping to hardware. They are implicitly always enabled.
    > > > *
    > > > * The cxl_mem_command is the driver's internal representation of commands that
    > > > * are supported by the driver. Some of these commands may not be supported by
    > > > @@ -129,6 +131,7 @@ struct cxl_mem_command {
    > > > #define CXL_CMD_INTERNAL_FLAG_NONE 0
    > > > #define CXL_CMD_INTERNAL_FLAG_HIDDEN BIT(0)
    > > > #define CXL_CMD_INTERNAL_FLAG_MANDATORY BIT(1)
    > > > +#define CXL_CMD_INTERNAL_FLAG_PSEUDO BIT(2)
    > > > };
    > > >
    > > > /*
    > > > @@ -140,7 +143,7 @@ struct cxl_mem_command {
    > > > static struct cxl_mem_command mem_commands[] = {
    > > > CXL_CMD(INVALID, KERNEL, 0, 0, HIDDEN),
    > > > CXL_CMD(IDENTIFY, NONE, 0, 0x43, MANDATORY),
    > > > - CXL_CMD(RAW, NONE, ~0, ~0, MANDATORY),
    > > > + CXL_CMD(RAW, NONE, ~0, ~0, PSEUDO),
    > > > };
    > > >
    > > > #define cxl_for_each_cmd(cmd) \
    > > > @@ -618,6 +621,10 @@ static int cxl_validate_cmd_from_user(struct cxl_mem *cxlm,
    > > > c = &mem_commands[send_cmd->id];
    > > > info = &c->info;
    > > >
    > > > + /* Check that the command is enabled for hardware */
    > > > + if (!test_bit(cxl_cmd_index(c), cxlm->enabled_cmds))
    > > > + return -ENOTTY;
    > > > +
    > > > if (info->flags & CXL_MEM_COMMAND_FLAG_KERNEL)
    > > > return -EPERM;
    > > >
    > > > @@ -1029,6 +1036,31 @@ static int cxl_mem_add_memdev(struct cxl_mem *cxlm)
    > > > return rc;
    > > > }
    > > >
    > > > +/**
    > > > + * cxl_mem_enumerate_cmds() - Enumerate commands for a device.
    > > > + * @cxlm: The device.
    > > > + *
    > > > + * Returns 0 if enumerate completed successfully.
    > > > + *
    > > > + * CXL devices have optional support for certain commands. This function will
    > > > + * determine the set of supported commands for the hardware and update the
    > > > + * enabled_cmds bitmap in the @cxlm.
    > > > + */
    > > > +static int cxl_mem_enumerate_cmds(struct cxl_mem *cxlm)
    > > > +{
    > > > + struct cxl_mem_command *c;
    > > > +
    > > > + /* All commands are considered enabled for now (except INVALID). */
    > > > + cxl_for_each_cmd(c) {
    > > > + if (c->flags & CXL_CMD_INTERNAL_FLAG_HIDDEN)
    > > > + continue;
    > > > +
    > > > + set_bit(cxl_cmd_index(c), cxlm->enabled_cmds);
    > > > + }
    > > > +
    > > > + return 0;
    > > > +}
    > > > +
    > > > /**
    > > > * cxl_mem_identify() - Send the IDENTIFY command to the device.
    > > > * @cxlm: The device to identify.
    > > > @@ -1147,6 +1179,10 @@ static int cxl_mem_probe(struct pci_dev *pdev, const struct pci_device_id *id)
    > > > if (rc)
    > > > goto err;
    > > >
    > > > + rc = cxl_mem_enumerate_cmds(cxlm);
    > > > + if (rc)
    > > > + return rc;
    > > > +
    > > > rc = cxl_mem_identify(cxlm);
    > > > if (rc)
    > > > goto err;
    > >

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