Re: [PATCH v4 3/4] remoteproc: imx_dsp_rproc: Add remoteproc driver for DSP on i.MX

[Shengjiu Wang <shengjiu.wang@gmail.com>]

On Fri, Sep 17, 2021 at 1:00 AM Mathieu Poirier
<mathieu.poirier@linaro.org> wrote:
>
> [...]
>
> > > > +
> > > > +/**
> > > > + * imx_dsp_rproc_elf_load_segments() - load firmware segments to memory
> > > > + * @rproc: remote processor which will be booted using these fw segments
> > > > + * @fw: the ELF firmware image
> > > > + *
> > > > + * This function specially checks if memsz is zero or not, otherwise it
> > > > + * is mostly same as rproc_elf_load_segments().
> > > > + */
> > > > +static int imx_dsp_rproc_elf_load_segments(struct rproc *rproc,
> > > > +                                        const struct firmware *fw)
> > > > +{
> > > > +     struct device *dev = &rproc->dev;
> > > > +     u8 class = fw_elf_get_class(fw);
> > > > +     u32 elf_phdr_get_size = elf_size_of_phdr(class);
> > > > +     const u8 *elf_data = fw->data;
> > > > +     const void *ehdr, *phdr;
> > > > +     int i, ret = 0;
> > > > +     u16 phnum;
> > > > +
> > > > +     ehdr = elf_data;
> > > > +     phnum = elf_hdr_get_e_phnum(class, ehdr);
> > > > +     phdr = elf_data + elf_hdr_get_e_phoff(class, ehdr);
> > > > +
> > > > +     /* go through the available ELF segments */
> > > > +     for (i = 0; i < phnum; i++, phdr += elf_phdr_get_size) {
> > > > +             u64 da = elf_phdr_get_p_paddr(class, phdr);
> > > > +             u64 memsz = elf_phdr_get_p_memsz(class, phdr);
> > > > +             u64 filesz = elf_phdr_get_p_filesz(class, phdr);
> > > > +             u64 offset = elf_phdr_get_p_offset(class, phdr);
> > > > +             u32 type = elf_phdr_get_p_type(class, phdr);
> > > > +             void *ptr;
> > > > +             bool is_iomem;
> > > > +
> > > > +             if (type != PT_LOAD || !memsz)
> > >
> > > You did a really good job with adding comments but this part is undocumented...
> > > If I read this correctly you need to check for !memsz because some part of
> > > the program segment may have a header but its memsz is zero, in which case it can
> > > be safely skipped.  So why is that segment in the image to start with, and why
> > > is it marked PT_LOAD if it is not needed?  This is very puzzling...
> >
> > Actually I have added comments in the header of this function.
>
> Indeed there is a mention of memsz in the function's header but it doesn't
> mention _why_ this is needed, and that is what I'm looking for.
>
> >
> > memsz= 0 with PT_LOAD issue, I have asked the toolchain's vendor,
> > they said that this case is allowed by elf spec...
> >
> > And in the "pru_rproc.c" and "mtk_scp.c", seems they met same problem
> > they also check the filesz in their internal xxx_elf_load_segments() function.
>
> In both cases they are skipping PT_LOAD sections where "filesz" is '0', which
> makes sense because we don't know how many bytes to copy.  But here you are
> skipping over a PT_LOAD section with a potentially valid filesz, and that is the
> part I don't understand.

Ok, I can use filesz instead. For my case, filesz = memsz = 0,
it is the same result I want.

The reason why I use "memsz '' is because there is  "if (filesz > memsz) "
check after this,  if memsz is zero, then "filesz" should be zero too, other
values are not allowed.

>
> >
> > >
> > >
> > > > +                     continue;
> > > > +
> > > > +             dev_dbg(dev, "phdr: type %d da 0x%llx memsz 0x%llx filesz 0x%llx\n",
> > > > +                     type, da, memsz, filesz);
> > > > +
> > > > +             if (filesz > memsz) {
> > > > +                     dev_err(dev, "bad phdr filesz 0x%llx memsz 0x%llx\n",
> > > > +                             filesz, memsz);
> > > > +                     ret = -EINVAL;
> > > > +                     break;
> > > > +             }
> > > > +
> > > > +             if (offset + filesz > fw->size) {
> > > > +                     dev_err(dev, "truncated fw: need 0x%llx avail 0x%zx\n",
> > > > +                             offset + filesz, fw->size);
> > > > +                     ret = -EINVAL;
> > > > +                     break;
> > > > +             }
> > > > +
> > > > +             if (!rproc_u64_fit_in_size_t(memsz)) {
> > > > +                     dev_err(dev, "size (%llx) does not fit in size_t type\n",
> > > > +                             memsz);
> > > > +                     ret = -EOVERFLOW;
> > > > +                     break;
> > > > +             }
> > > > +
> > > > +             /* grab the kernel address for this device address */
> > > > +             ptr = rproc_da_to_va(rproc, da, memsz, &is_iomem);
> > >
> > >                 rproc_da_to_va(rproc, da, memsz, NULL);
> >
> > yes, will update it.
> >
> > >
> > > More comments to follow later today or tomorrow.
> >
> > Thanks.
> >
> > Best regards
> > Wang Shengjiu