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

Shengjiu Wang
2021-09-17T09:45:03Z

On Fri, Sep 17, 2021 at 1:20 PM Shengjiu Wang <shengjiu.wang@gmail.com> wrote:
>
> 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.

But I still think checking "!memsz" is better than filesz, because
memsz > filesz is allowed (filesz = 0), the code below can be executed.
filesz > memsz is not allowed.

What do you think?

Best regards
Wang shengjiu
>
> >
> > >
> > > >
> > > >
> > > > > + 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