RE: [RFC PATCH v2 13/20] hw/arm/smmuv3-accel: Introduce helpers to batch and issue cache invalidations

[Shameerali Kolothum Thodi via <qemu-devel@nongnu.org>]

> -----Original Message-----
> From: Donald Dutile <ddutile@redhat.com>
> Sent: Wednesday, March 19, 2025 1:31 AM
> To: Shameerali Kolothum Thodi
> <shameerali.kolothum.thodi@huawei.com>; qemu-arm@nongnu.org;
> qemu-devel@nongnu.org
> Cc: eric.auger@redhat.com; peter.maydell@linaro.org; jgg@nvidia.com;
> nicolinc@nvidia.com; berrange@redhat.com; nathanc@nvidia.com;
> mochs@nvidia.com; smostafa@google.com; Linuxarm
> <linuxarm@huawei.com>; Wangzhou (B) <wangzhou1@hisilicon.com>;
> jiangkunkun <jiangkunkun@huawei.com>; Jonathan Cameron
> <jonathan.cameron@huawei.com>; zhangfei.gao@linaro.org
> Subject: Re: [RFC PATCH v2 13/20] hw/arm/smmuv3-accel: Introduce helpers
> to batch and issue cache invalidations
> 
> Shameer,
> 
> Hi,
> 
> 
> On 3/11/25 10:10 AM, Shameer Kolothum wrote:
> > From: Nicolin Chen <nicolinc@nvidia.com>
> >
> > Inroduce an SMMUCommandBatch and some helpers to batch and issue
> the
>    ^^^^^^^^ Introduce
> > commands.  Currently separate out TLBI commands and device cache
> > commands to avoid some errata on certain versions of SMMUs. Later it
> > should check IIDR register to detect if underlying SMMU hw has such an
> erratum.
> Where is all this info about 'certain versions of SMMUs' and 'check IIDR
> register' has something to do with 'underlying SMMU hw such an erratum',
> -- which IIDR (& bits)? or are we talking about rsvd SMMU_IDR<> registers?

I guess the batching has constraints on some platforms, IIRC, this was discussed
somewhere in a kernel thread.  

Nicolin, could you please provide some background on this.

> 
> And can't these helpers be used for emulated smmuv3 as well as
> accelerated?

Could be I guess. But no benefit in terms of performance. May be will make
code look nicer. I will take a look if not much of changes in the emulated path.

Thanks,
Shameer