linux-kernel - Re: [PATCH 2/3] firmware: qcom_scm: Cleanup code in qcom_scm_assign

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Date:   Mon, 22 Jul 2019 17:04:57 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Andy Gross <agross@...nel.org>, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        Ian Jackson <ian.jackson@...rix.com>,
        Julien Grall <julien.grall@....com>,
        Avaneesh Kumar Dwivedi <akdwived@...eaurora.org>
Subject: Re: [PATCH 2/3] firmware: qcom_scm: Cleanup code in qcom_scm_assign_mem()

Quoting Bjorn Andersson (2019-07-22 16:27:19)
> On Fri 17 May 14:09 PDT 2019, Stephen Boyd wrote:
> 
> > There are some questionable coding styles in this function. It looks
> > quite odd to deref a pointer with array indexing that only uses the
> > first element. Also, destroying an input/output variable halfway through
> > the function and then overwriting it on success is not clear. It's
> > better to use a local variable and the kernel macros to step through
> > each bit set in a bitmask and clearly show where outputs are set.
> > 
> > Cc: Ian Jackson <ian.jackson@...rix.com>
> > Cc: Julien Grall <julien.grall@....com>
> > Cc: Bjorn Andersson <bjorn.andersson@...aro.org>
> > Cc: Avaneesh Kumar Dwivedi <akdwived@...eaurora.org>
> > Signed-off-by: Stephen Boyd <swboyd@...omium.org>
> > ---
> >  drivers/firmware/qcom_scm.c | 34 ++++++++++++++++------------------
> >  include/linux/qcom_scm.h    |  9 +++++----
> >  2 files changed, 21 insertions(+), 22 deletions(-)
> > 
> > diff --git a/drivers/firmware/qcom_scm.c b/drivers/firmware/qcom_scm.c
> > index 0c63495cf269..153f13f72bac 100644
> > --- a/drivers/firmware/qcom_scm.c
> > +++ b/drivers/firmware/qcom_scm.c
> > @@ -443,7 +443,8 @@ EXPORT_SYMBOL(qcom_scm_set_remote_state);
> >   */
> >  int qcom_scm_assign_mem(phys_addr_t mem_addr, size_t mem_sz,
> >                       unsigned int *srcvm,
> > -                     struct qcom_scm_vmperm *newvm, int dest_cnt)
> > +                     const struct qcom_scm_vmperm *newvm,
> > +                     unsigned int dest_cnt)
> >  {
> >       struct qcom_scm_current_perm_info *destvm;
> >       struct qcom_scm_mem_map_info *mem_to_map;
> > @@ -458,11 +459,10 @@ int qcom_scm_assign_mem(phys_addr_t mem_addr, size_t mem_sz,
> >       int next_vm;
> >       __le32 *src;
> >       void *ptr;
> > -     int ret;
> > -     int len;
> > -     int i;
> > +     int ret, i, b;
> > +     unsigned long srcvm_bits = *srcvm;
> >  
> > -     src_sz = hweight_long(*srcvm) * sizeof(*src);
> > +     src_sz = hweight_long(srcvm_bits) * sizeof(*src);
> >       mem_to_map_sz = sizeof(*mem_to_map);
> >       dest_sz = dest_cnt * sizeof(*destvm);
> >       ptr_sz = ALIGN(src_sz, SZ_64) + ALIGN(mem_to_map_sz, SZ_64) +
> > @@ -475,28 +475,26 @@ int qcom_scm_assign_mem(phys_addr_t mem_addr, size_t mem_sz,
> >  
> >       /* Fill source vmid detail */
> >       src = ptr;
> > -     len = hweight_long(*srcvm);
> > -     for (i = 0; i < len; i++) {
> > -             src[i] = cpu_to_le32(ffs(*srcvm) - 1);
> > -             *srcvm ^= 1 << (ffs(*srcvm) - 1);
> > -     }
> > +     i = 0;
> > +     for_each_set_bit(b, &srcvm_bits, sizeof(srcvm_bits))
> 
> The modem is sad that you only pass 8 here. Changed it to BITS_PER_LONG
> to include the modem's permission bit and applied all three patches.
> 

Ah of course. Thanks.

BTW, srcvm is an unsigned int, but then we do a bunch of unsigned long
operations on them. Maybe the whole API should be changed to be more
explicit about the size of the type, i.e. u64?