linux-kernel - Re: [PATCH v2 2/3] platform/x86/intel/tpmi: Add debugfs interface

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Date:   Wed, 12 Jul 2023 16:06:50 -0700
From:   srinivas pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     hdegoede@...hat.com, markgross@...nel.org,
        ilpo.jarvinen@...ux.intel.com, platform-driver-x86@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] platform/x86/intel/tpmi: Add debugfs interface

On Wed, 2023-07-12 at 18:13 +0300, Andy Shevchenko wrote:
> On Tue, Jul 11, 2023 at 03:09:48PM -0700, Srinivas Pandruvada wrote:
> > Add debugfs interface for debugging TPMI configuration and register
> > contents. This shows PFS (PM Feature structure) for each TPMI
> > device.
> > 
> > For each feature, show full register contents and allow to modify
> > register at an offset.
> > 
> > This debugfs interface is not present on locked down kernel with no
> > DEVMEM access and without CAP_SYS_RAWIO permission.
> 
> ...
> 
> >  struct intel_tpmi_pm_feature {
> >         struct intel_tpmi_pfs_entry pfs_header;
> >         unsigned int vsec_offset;
> > +       struct intel_vsec_device *vsec_dev;
> 
> Hmm... I don't know the layout of pfs_header, but this may be 4 bytes
> less
> if you move it upper.
The pfs_header is packed with size of 64 bit. So size will not change.
 
> 
> >  };
> 
> ...
> 
> > +       for (count = 0; count < pfs->pfs_header.num_entries;
> > ++count) {
> 
> > +               size = pfs->pfs_header.entry_size * sizeof(u32);
> 
> You already used this once, perhaps a macro helper?
> Also you can add there a comment that this comes from the trusted hw.
> 
Added.

> > +               /* The size is from a trusted hardware, but verify
> > anyway */
> > +               if (size > TPMI_MAX_BUFFER_SIZE) {
> > +                       /*
> > +                        * The next offset depends on the current
> > size. So, can't skip to the
> > +                        * display of the next entry. Simply return
> > from this function with error.
> > +                        */
> > +                       ret = -EIO;
> > +                       goto done_mem_show;
> > +               }
> > +
> > +               buffer = kmalloc(size, GFP_KERNEL);
> > +               if (!buffer) {
> > +                       ret = -ENOMEM;
> > +                       goto done_mem_show;
> > +               }
> > +
> > +               seq_printf(s, "TPMI Instance:%d offset:0x%x\n",
> > count, off);
> > +
> > +               mem = ioremap(off, size);
> > +               if (!mem) {
> > +                       ret = -ENOMEM;
> > +                       kfree(buffer);
> > +                       goto done_mem_show;
> > +               }
> > +
> > +               memcpy_fromio(buffer, mem, size);
> > +
> > +               seq_hex_dump(s, " ", DUMP_PREFIX_OFFSET, row_size,
> > sizeof(u32), buffer, size,
> > +                            false);
> > +
> > +               iounmap(mem);
> > +               kfree(buffer);
> > +
> > +               off += size;
> > +       }
> > +
> > +done_mem_show:
> > +       mutex_unlock(&tpmi_dev_lock);
> > +
> > +       return ret;
> > +}
> 
> ...
> 
> > +       size = pfs->pfs_header.entry_size * sizeof(u32);
> > +       if (size > TPMI_MAX_BUFFER_SIZE)
> > +               return -EIO;
> 
> Again a dup even with a check.
> 
> ...
> 
> > +       top_dir = debugfs_create_dir(name, NULL);
> > +       if (IS_ERR_OR_NULL(top_dir))
> 
> I dunno if I told you, but after a discussion (elsewhere), I realized
> two things:
> 1) this one never returns NULL;
> 2) even if error pointer is returned, the debugfs API is aware and
>    will do nothing.
> 
> Hence this conditional is redundant.
Removed that. My original version didn't check the return value.

> 
> > +               return;
> 
> ...
> 
> > +       for (i = 0; i < tpmi_info->feature_count; ++i) {
> 
> Why preincrement?
Does it matter for a "for" loop increment?

Thanks,
Srinivas
> 
> > +               struct intel_tpmi_pm_feature *pfs;
> > +               struct dentry *dir;
> > +
> > +               pfs = &tpmi_info->tpmi_features[i];
> > +               snprintf(name, sizeof(name), "tpmi-id-%02x", pfs-
> > >pfs_header.tpmi_id);
> > +               dir = debugfs_create_dir(name, top_dir);
> > +
> > +               debugfs_create_file("mem_dump", 0444, dir, pfs,
> > &tpmi_mem_dump_fops);
> > +               debugfs_create_file("mem_write", 0644, dir, pfs,
> > &mem_write_ops);
> > +       }
>