linux-kernel - Re: [PATCH v2 11/11] firmware: qcom: scm: enable SHM bridge

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Message-ID: <CAMRc=MdMd7CGWEvDbcYRTHZaLpAYdKyR6wEuFTKux6T+C3UU+Q@mail.gmail.com>
Date:   Thu, 28 Sep 2023 20:28:40 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Elliot Berman <quic_eberman@...cinc.com>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Maximilian Luz <luzmaximilian@...il.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        kernel@...cinc.com,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v2 11/11] firmware: qcom: scm: enable SHM bridge

On Thu, Sep 28, 2023 at 7:10 PM Elliot Berman <quic_eberman@...cinc.com> wrote:
>
>
>
> On 9/28/2023 2:20 AM, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> >
> > Extens the SCM memory allocator with using the SHM Bridge feature if
> > available on the platform. This makes the trustzone only use dedicated
> > buffers for SCM calls. We map the entire SCM genpool as a bridge.
> >
> > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > ---
> >  drivers/firmware/qcom/qcom_scm-mem.c | 42 ++++++++++++++++++++++++++--
> >  1 file changed, 39 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/firmware/qcom/qcom_scm-mem.c b/drivers/firmware/qcom/qcom_scm-mem.c
> > index eafecbe23770..12b12b15f46f 100644
> > --- a/drivers/firmware/qcom/qcom_scm-mem.c
> > +++ b/drivers/firmware/qcom/qcom_scm-mem.c
> > @@ -16,6 +16,8 @@
> >
> >  #include "qcom_scm.h"
> >
> > +#define QCOM_SHM_BRIDGE_NUM_VM_SHIFT 9
> > +
> >  static size_t qcom_scm_mem_pool_size = SZ_2M;
> >  module_param_named(qcom_scm_mem_pool_size, qcom_scm_mem_pool_size,
> >                  ulong, 0400);
> > @@ -108,8 +110,24 @@ phys_addr_t qcom_scm_mem_to_phys(void *vaddr)
> >       return chunk->paddr;
> >  }
> >
> > +static int qcom_scm_mem_shm_bridge_create(void)
> > +{
> > +     uint64_t pfn_and_ns_perm, ipfn_and_s_perm, size_and_flags, ns_perms;
> > +
> > +     ns_perms = (QCOM_SCM_PERM_WRITE | QCOM_SCM_PERM_READ);
> > +     pfn_and_ns_perm = (u64)qcom_scm_mem.pbase | ns_perms;
> > +     ipfn_and_s_perm = (u64)qcom_scm_mem.pbase | ns_perms;
> > +     size_and_flags = qcom_scm_mem.size | (1 << QCOM_SHM_BRIDGE_NUM_VM_SHIFT);
> > +
> > +     return qcom_scm_create_shm_bridge(qcom_scm_mem.dev, pfn_and_ns_perm,
> > +                                       ipfn_and_s_perm, size_and_flags,
> > +                                       QCOM_SCM_VMID_HLOS);
> > +}
> > +
> >  int qcom_scm_mem_enable(struct device *dev)
> >  {
> > +     int ret;
> > +
> >       INIT_RADIX_TREE(&qcom_scm_mem.chunks, GFP_ATOMIC);
> >       spin_lock_init(&qcom_scm_mem.lock);
> >       qcom_scm_mem.dev = dev;
> > @@ -128,7 +146,25 @@ int qcom_scm_mem_enable(struct device *dev)
> >
> >       gen_pool_set_algo(qcom_scm_mem.pool, gen_pool_best_fit, NULL);
> >
> > -     return gen_pool_add_virt(qcom_scm_mem.pool,
> > -                              (unsigned long)qcom_scm_mem.vbase,
> > -                              qcom_scm_mem.pbase, qcom_scm_mem.size, -1);
> > +     ret = gen_pool_add_virt(qcom_scm_mem.pool,
> > +                             (unsigned long)qcom_scm_mem.vbase,
> > +                             qcom_scm_mem.pbase, qcom_scm_mem.size, -1);
> > +     if (ret)
> > +             return ret;
> > +
> > +     ret = qcom_scm_enable_shm_bridge();
> > +     if (ret) {
> > +             if (ret == EOPNOTSUPP)
> > +                     dev_info(dev, "SHM Bridge not supported\n");
> > +             else
> > +                     return ret;
> > +     } else {
> > +             ret = qcom_scm_mem_shm_bridge_create();
> > +             if (ret)
> > +                     return ret;
> > +
> > +             dev_info(dev, "SHM Bridge enabled\n");
>
> Do you need to add clean up (deletion) of the SHM bridge on driver remove?
>
> One easy approach I could think: implemnet devm_qcom_scm_mem_shm_bridge_create
> which calls qcom_scm_delete_shm_bridge on the clean up
> (qcom_scm_delete_shm_bridge implemented in downstream, not in this series).
>

There wouldn't be any user of these symbols yet so let's think about
it when there's a valid use-case upstream.

Bart

> > +     }
> > +
> > +     return 0;
> >  }