linux-kernel - Re: [PATCH] gpu: drm: i915: Change return type to vm_fault

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Message-ID: <CAFqt6zb_XqVKHPH5U4TubgDTgBURWv63cfa_OMQEyHjGZpKTHQ@mail.gmail.com>
Date:   Tue, 17 Apr 2018 21:14:32 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     Jani Nikula <jani.nikula@...ux.intel.com>
Cc:     joonas.lahtinen@...ux.intel.com, rodrigo.vivi@...el.com,
        airlied@...ux.ie, intel-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH] gpu: drm: i915: Change return type to vm_fault_t

Not exactly. The plan for these patches is to introduce new vm_fault_t type
in vm_operations_struct fault handlers. It's now available in 4.17-rc1. We will
push all the required drivers/filesystem changes through different maintainers
to linus tree. Once everything is converted into vm_fault_t type then Changing
it from a signed to an unsigned int causes GCC to warn about an assignment
from an incompatible type -- int foo(void) is incompatible with
unsigned int foo(void).

Please refer 1c8f422059ae ("mm: change return type to vm_fault_t") in 4.17-rc1.

On Tue, Apr 17, 2018 at 8:59 PM, Jani Nikula
<jani.nikula@...ux.intel.com> wrote:
> On Tue, 17 Apr 2018, Souptick Joarder <jrdr.linux@...il.com> wrote:
>> Use new return type vm_fault_t for fault handler. For
>> now, this is just documenting that the function returns
>> a VM_FAULT value rather than an errno. Once all instances
>> are converted, vm_fault_t will become a distinct type.
>>
>> Reference id -> 1c8f422059ae ("mm: change return type to
>> vm_fault_t")
>>
>> Signed-off-by: Souptick Joarder <jrdr.linux@...il.com>
>> ---
>>  drivers/gpu/drm/i915/i915_drv.h |  3 ++-
>>  drivers/gpu/drm/i915/i915_gem.c | 15 ++++++++-------
>>  2 files changed, 10 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
>> index a42deeb..95b0d50 100644
>> --- a/drivers/gpu/drm/i915/i915_drv.h
>> +++ b/drivers/gpu/drm/i915/i915_drv.h
>> @@ -51,6 +51,7 @@
>>  #include <drm/drm_gem.h>
>>  #include <drm/drm_auth.h>
>>  #include <drm/drm_cache.h>
>> +#include <linux/mm_types.h>
>>
>>  #include "i915_params.h"
>>  #include "i915_reg.h"
>> @@ -3363,7 +3364,7 @@ int i915_gem_wait_for_idle(struct drm_i915_private *dev_priv,
>>                          unsigned int flags);
>>  int __must_check i915_gem_suspend(struct drm_i915_private *dev_priv);
>>  void i915_gem_resume(struct drm_i915_private *dev_priv);
>> -int i915_gem_fault(struct vm_fault *vmf);
>> +vm_fault_t i915_gem_fault(struct vm_fault *vmf);
>>  int i915_gem_object_wait(struct drm_i915_gem_object *obj,
>>                        unsigned int flags,
>>                        long timeout,
>> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
>> index dd89abd..bdac690 100644
>> --- a/drivers/gpu/drm/i915/i915_gem.c
>> +++ b/drivers/gpu/drm/i915/i915_gem.c
>> @@ -1882,7 +1882,7 @@ int i915_gem_mmap_gtt_version(void)
>>   * The current feature set supported by i915_gem_fault() and thus GTT mmaps
>>   * is exposed via I915_PARAM_MMAP_GTT_VERSION (see i915_gem_mmap_gtt_version).
>>   */
>> -int i915_gem_fault(struct vm_fault *vmf)
>> +vm_fault_t i915_gem_fault(struct vm_fault *vmf)
>>  {
>>  #define MIN_CHUNK_PAGES ((1 << 20) >> PAGE_SHIFT) /* 1 MiB */
>>       struct vm_area_struct *area = vmf->vma;
>> @@ -1895,6 +1895,7 @@ int i915_gem_fault(struct vm_fault *vmf)
>>       pgoff_t page_offset;
>>       unsigned int flags;
>>       int ret;
>> +     vm_fault_t retval;
>
> What's the point of changing the name? An unnecessary change.
>
> BR,
> Jani.
>
>>
>>       /* We don't use vmf->pgoff since that has the fake offset */
>>       page_offset = (vmf->address - area->vm_start) >> PAGE_SHIFT;
>> @@ -2000,7 +2001,7 @@ int i915_gem_fault(struct vm_fault *vmf)
>>                * and so needs to be reported.
>>                */
>>               if (!i915_terminally_wedged(&dev_priv->gpu_error)) {
>> -                     ret = VM_FAULT_SIGBUS;
>> +                     retval = VM_FAULT_SIGBUS;
>>                       break;
>>               }
>>       case -EAGAIN:
>> @@ -2017,21 +2018,21 @@ int i915_gem_fault(struct vm_fault *vmf)
>>                * EBUSY is ok: this just means that another thread
>>                * already did the job.
>>                */
>> -             ret = VM_FAULT_NOPAGE;
>> +             retval = VM_FAULT_NOPAGE;
>>               break;
>>       case -ENOMEM:
>> -             ret = VM_FAULT_OOM;
>> +             retval = VM_FAULT_OOM;
>>               break;
>>       case -ENOSPC:
>>       case -EFAULT:
>> -             ret = VM_FAULT_SIGBUS;
>> +             retval = VM_FAULT_SIGBUS;
>>               break;
>>       default:
>>               WARN_ONCE(ret, "unhandled error in i915_gem_fault: %i\n", ret);
>> -             ret = VM_FAULT_SIGBUS;
>> +             retval = VM_FAULT_SIGBUS;
>>               break;
>>       }
>> -     return ret;
>> +     return retval;
>>  }
>>
>>  static void __i915_gem_object_release_mmap(struct drm_i915_gem_object *obj)
>> --
>> 1.9.1
>>
>
> --
> Jani Nikula, Intel Open Source Technology Center