Re: [RESEND PATCH 2/2] hw/cxl: Fix incorrect reset of commit and associated clearing of committed.

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Wed, 22 Mar 2023 16:21:26 +0000
Fan Ni <fan.ni@samsung.com> wrote:

> On Wed, Mar 22, 2023 at 10:33:00AM +0000, Jonathan Cameron wrote:
> > The hardware clearing the commit bit is not spec compliant.
> > Clearing of committed bit when commit is cleared is not specifically
> > stated in the CXL spec, but is the expected (and simplest) permitted
> > behaviour so use that for QEMU emulation.
> > 
> > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > ---  
> 
> Reviewed-by: Fan Ni <fan.ni@samsung.com>
> Tested-by: Fan Ni <fan.ni@samsung.com>
> 
> 
> The patch passed the tests as shown in previous mailing list discussion:
> https://lore.kernel.org/linux-cxl/640276695c8e8_5b27929473@dwillia2-xfh.jf.intel.com.notmuch/T/#m0afcfc21d68c84c07f2e9e3194f587c2ffa82d6d
> The following two topologies are tested:
> 1. one HB with one root port and a direct attached memdev.
> 2. one HB with 2 root ports and a memdev is directly attached to a CXL switch
> which is attached to one root port.
> 
> One minor thing below.
> 
> >  hw/cxl/cxl-component-utils.c |  6 +++++-
> >  hw/mem/cxl_type3.c           | 21 ++++++++++++++++++++-
> >  2 files changed, 25 insertions(+), 2 deletions(-)
> > 
> > diff --git a/hw/cxl/cxl-component-utils.c b/hw/cxl/cxl-component-utils.c
> > index a3e6cf75cf..378f1082ce 100644
> > --- a/hw/cxl/cxl-component-utils.c
> > +++ b/hw/cxl/cxl-component-utils.c
> > @@ -38,19 +38,23 @@ static void dumb_hdm_handler(CXLComponentState *cxl_cstate, hwaddr offset,
> >      ComponentRegisters *cregs = &cxl_cstate->crb;
> >      uint32_t *cache_mem = cregs->cache_mem_registers;
> >      bool should_commit = false;
> > +    bool should_uncommit = false;
> >  
> >      switch (offset) {
> >      case A_CXL_HDM_DECODER0_CTRL:
> >          should_commit = FIELD_EX32(value, CXL_HDM_DECODER0_CTRL, COMMIT);
> > +        should_uncommit = !should_commit;  
> This will cause committed always reset if COMMIT is 0, not only
> 1->0. No issue for now, just point out to make sure it is what we
> want.

True.  However I think it's harmless.

We will want to be a little careful if uncommitting gains other
functionality in future though.

Note that the same potential corner existing on the commit side of things.
Trying to commit a decoder that is already committed will call the code
for commit (also currently harmless)

I'm not particularly keen to introduce additional complexity to separate
out these cases until / if we ever need it.

Jonathan

> >          break;
> >      default:
> >          break;
> >      }
> >  
> >      if (should_commit) {
> > -        value = FIELD_DP32(value, CXL_HDM_DECODER0_CTRL, COMMIT, 0);
> >          value = FIELD_DP32(value, CXL_HDM_DECODER0_CTRL, ERR, 0);
> >          value = FIELD_DP32(value, CXL_HDM_DECODER0_CTRL, COMMITTED, 1);
> > +    } else if (should_uncommit) {
> > +        value = FIELD_DP32(value, CXL_HDM_DECODER0_CTRL, ERR, 0);
> > +        value = FIELD_DP32(value, CXL_HDM_DECODER0_CTRL, COMMITTED, 0);
> >      }
> >      stl_le_p((uint8_t *)cache_mem + offset, value);
> >  }
> > diff --git a/hw/mem/cxl_type3.c b/hw/mem/cxl_type3.c
> > index 846089ccda..9598d584ac 100644
> > --- a/hw/mem/cxl_type3.c
> > +++ b/hw/mem/cxl_type3.c
> > @@ -320,13 +320,28 @@ static void hdm_decoder_commit(CXLType3Dev *ct3d, int which)
> >  
> >      ctrl = ldl_le_p(cache_mem + R_CXL_HDM_DECODER0_CTRL);
> >      /* TODO: Sanity checks that the decoder is possible */
> > -    ctrl = FIELD_DP32(ctrl, CXL_HDM_DECODER0_CTRL, COMMIT, 0);
> >      ctrl = FIELD_DP32(ctrl, CXL_HDM_DECODER0_CTRL, ERR, 0);
> >      ctrl = FIELD_DP32(ctrl, CXL_HDM_DECODER0_CTRL, COMMITTED, 1);
> >  
> >      stl_le_p(cache_mem + R_CXL_HDM_DECODER0_CTRL, ctrl);
> >  }
> >  
> > +static void hdm_decoder_uncommit(CXLType3Dev *ct3d, int which)
> > +{
> > +    ComponentRegisters *cregs = &ct3d->cxl_cstate.crb;
> > +    uint32_t *cache_mem = cregs->cache_mem_registers;
> > +    uint32_t ctrl;
> > +
> > +    assert(which == 0);
> > +
> > +    ctrl = ldl_le_p(cache_mem + R_CXL_HDM_DECODER0_CTRL);
> > +
> > +    ctrl = FIELD_DP32(ctrl, CXL_HDM_DECODER0_CTRL, ERR, 0);
> > +    ctrl = FIELD_DP32(ctrl, CXL_HDM_DECODER0_CTRL, COMMITTED, 0);
> > +
> > +    stl_le_p(cache_mem + R_CXL_HDM_DECODER0_CTRL, ctrl);
> > +}
> > +
> >  static int ct3d_qmp_uncor_err_to_cxl(CxlUncorErrorType qmp_err)
> >  {
> >      switch (qmp_err) {
> > @@ -395,6 +410,7 @@ static void ct3d_reg_write(void *opaque, hwaddr offset, uint64_t value,
> >      CXLType3Dev *ct3d = container_of(cxl_cstate, CXLType3Dev, cxl_cstate);
> >      uint32_t *cache_mem = cregs->cache_mem_registers;
> >      bool should_commit = false;
> > +    bool should_uncommit = false;
> >      int which_hdm = -1;
> >  
> >      assert(size == 4);
> > @@ -403,6 +419,7 @@ static void ct3d_reg_write(void *opaque, hwaddr offset, uint64_t value,
> >      switch (offset) {
> >      case A_CXL_HDM_DECODER0_CTRL:
> >          should_commit = FIELD_EX32(value, CXL_HDM_DECODER0_CTRL, COMMIT);
> > +        should_uncommit = !should_commit;
> >          which_hdm = 0;
> >          break;
> >      case A_CXL_RAS_UNC_ERR_STATUS:
> > @@ -489,6 +506,8 @@ static void ct3d_reg_write(void *opaque, hwaddr offset, uint64_t value,
> >      stl_le_p((uint8_t *)cache_mem + offset, value);
> >      if (should_commit) {
> >          hdm_decoder_commit(ct3d, which_hdm);
> > +    } else if (should_uncommit) {
> > +        hdm_decoder_uncommit(ct3d, which_hdm);
> >      }
> >  }
> >  
> > -- 
> > 2.37.2
> >