On Tue, Nov 15, 2022 at 11:26:11AM -0800, Lucas De Marchi wrote: > There were several updates in the driver on how the workarounds are > handled since its documentation was written. Update the documentation to > reflect the current reality. > > v2: > - Remove footnote that was wrongly referenced, adding back the > reference in the correct paragraph. > - Remove "Display workarounds" and just mention "display IP" under > "Other" category since all of them are peppered around the driver. > > Cc: Matt Roper <matthew.d.roper@xxxxxxxxx> > Signed-off-by: Lucas De Marchi <lucas.demarchi@xxxxxxxxx> > Acked-by: Balasubramani Vivekanandan <balasubramani.vivekanandan@xxxxxxxxx> # v1 Reviewed-by: Matt Roper <matthew.d.roper@xxxxxxxxx> > --- > drivers/gpu/drm/i915/gt/intel_workarounds.c | 80 +++++++++++++-------- > 1 file changed, 50 insertions(+), 30 deletions(-) > > diff --git a/drivers/gpu/drm/i915/gt/intel_workarounds.c b/drivers/gpu/drm/i915/gt/intel_workarounds.c > index 213160f29ec3..290f9f91fdf4 100644 > --- a/drivers/gpu/drm/i915/gt/intel_workarounds.c > +++ b/drivers/gpu/drm/i915/gt/intel_workarounds.c > @@ -18,42 +18,62 @@ > /** > * DOC: Hardware workarounds > * > - * This file is intended as a central place to implement most [1]_ of the > - * required workarounds for hardware to work as originally intended. They fall > - * in five basic categories depending on how/when they are applied: > + * Hardware workarounds are register programming documented to be executed in > + * the driver that fall outside of the normal programming sequences for a > + * platform. There are some basic categories of workarounds, depending on > + * how/when they are applied: > * > - * - Workarounds that touch registers that are saved/restored to/from the HW > - * context image. The list is emitted (via Load Register Immediate commands) > - * everytime a new context is created. > - * - GT workarounds. The list of these WAs is applied whenever these registers > - * revert to default values (on GPU reset, suspend/resume [2]_, etc..). > - * - Display workarounds. The list is applied during display clock-gating > - * initialization. > - * - Workarounds that whitelist a privileged register, so that UMDs can manage > - * them directly. This is just a special case of a MMMIO workaround (as we > - * write the list of these to/be-whitelisted registers to some special HW > - * registers). > - * - Workaround batchbuffers, that get executed automatically by the hardware > - * on every HW context restore. > + * - Context workarounds: workarounds that touch registers that are > + * saved/restored to/from the HW context image. The list is emitted (via Load > + * Register Immediate commands) once when initializing the device and saved in > + * the default context. That default context is then used on every context > + * creation to have a "primed golden context", i.e. a context image that > + * already contains the changes needed to all the registers. > * > - * .. [1] Please notice that there are other WAs that, due to their nature, > - * cannot be applied from a central place. Those are peppered around the rest > - * of the code, as needed. > + * - Engine workarounds: the list of these WAs is applied whenever the specific > + * engine is reset. It's also possible that a set of engine classes share a > + * common power domain and they are reset together. This happens on some > + * platforms with render and compute engines. In this case (at least) one of > + * them need to keeep the workaround programming: the approach taken in the > + * driver is to tie those workarounds to the first compute/render engine that > + * is registered. When executing with GuC submission, engine resets are > + * outside of kernel driver control, hence the list of registers involved in > + * written once, on engine initialization, and then passed to GuC, that > + * saves/restores their values before/after the reset takes place. See > + * ``drivers/gpu/drm/i915/gt/uc/intel_guc_ads.c`` for reference. > * > - * .. [2] Technically, some registers are powercontext saved & restored, so they > - * survive a suspend/resume. In practice, writing them again is not too > - * costly and simplifies things. We can revisit this in the future. > + * - GT workarounds: the list of these WAs is applied whenever these registers > + * revert to their default values: on GPU reset, suspend/resume [1]_, etc. > + * > + * - Register whitelist: some workarounds need to be implemented in userspace, > + * but need to touch privileged registers. The whitelist in the kernel > + * instructs the hardware to allow the access to happen. From the kernel side, > + * this is just a special case of a MMIO workaround (as we write the list of > + * these to/be-whitelisted registers to some special HW registers). > + * > + * - Workaround batchbuffers: buffers that get executed automatically by the > + * hardware on every HW context restore. These buffers are created and > + * programmed in the default context so the hardware always go through those > + * programming sequences when switching contexts. The support for workaround > + * batchbuffers is enabled these hardware mechanisms: > * > - * Layout > - * ~~~~~~ > + * #. INDIRECT_CTX: A batchbuffer and an offset are provided in the default > + * context, pointing the hardware to jump to that location when that offset > + * is reached in the context restore. Workaround batchbuffer in the driver > + * currently uses this mechanism for all platforms. > * > - * Keep things in this file ordered by WA type, as per the above (context, GT, > - * display, register whitelist, batchbuffer). Then, inside each type, keep the > - * following order: > + * #. BB_PER_CTX_PTR: A batchbuffer is provided in the default context, > + * pointing the hardware to a buffer to continue executing after the > + * engine registers are restored in a context restore sequence. This is > + * currently not used in the driver. > * > - * - Infrastructure functions and macros > - * - WAs per platform in standard gen/chrono order > - * - Public functions to init or apply the given workaround type. > + * - Other: There are WAs that, due to their nature, cannot be applied from a > + * central place. Those are peppered around the rest of the code, as needed. > + * Workarounds related to the display IP are the main example. > + * > + * .. [1] Technically, some registers are powercontext saved & restored, so they > + * survive a suspend/resume. In practice, writing them again is not too > + * costly and simplifies things, so it's the approach taken in the driver. > */ > > static void wa_init_start(struct i915_wa_list *wal, struct intel_gt *gt, > -- > 2.38.1 > -- Matt Roper Graphics Software Engineer VTT-OSGC Platform Enablement Intel Corporation
