[v3,18/19] firmware: Add request_partial_firmware_into_buf()
diff mbox series

Message ID 20200724213640.389191-19-keescook@chromium.org
State New
Headers show
Series
  • Introduce partial kernel_read_file() support
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Commit Message

Kees Cook July 24, 2020, 9:36 p.m. UTC
From: Scott Branden <scott.branden@broadcom.com>

Add request_partial_firmware_into_buf() to allow for portions of a
firmware file to be read into a buffer. This is needed when large firmware
must be loaded in portions from a file on memory constrained systems.

Signed-off-by: Scott Branden <scott.branden@broadcom.com>
Co-developed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/base/firmware_loader/firmware.h |   4 +
 drivers/base/firmware_loader/main.c     | 109 +++++++++++++++++++-----
 include/linux/firmware.h                |  12 +++
 3 files changed, 105 insertions(+), 20 deletions(-)

Comments

Luis Chamberlain July 29, 2020, 1:17 a.m. UTC | #1
Long ago Takashi had some points about this strategy breaking
compressed file use. Was that considered?

  Luis

On Fri, Jul 24, 2020 at 02:36:39PM -0700, Kees Cook wrote:
> From: Scott Branden <scott.branden@broadcom.com>
> 
> Add request_partial_firmware_into_buf() to allow for portions of a
> firmware file to be read into a buffer. This is needed when large firmware
> must be loaded in portions from a file on memory constrained systems.
> 
> Signed-off-by: Scott Branden <scott.branden@broadcom.com>
> Co-developed-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  drivers/base/firmware_loader/firmware.h |   4 +
>  drivers/base/firmware_loader/main.c     | 109 +++++++++++++++++++-----
>  include/linux/firmware.h                |  12 +++
>  3 files changed, 105 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/base/firmware_loader/firmware.h b/drivers/base/firmware_loader/firmware.h
> index 7ad5fe52bc72..3f6eda46b3a2 100644
> --- a/drivers/base/firmware_loader/firmware.h
> +++ b/drivers/base/firmware_loader/firmware.h
> @@ -32,6 +32,8 @@
>   * @FW_OPT_FALLBACK_PLATFORM: Enable fallback to device fw copy embedded in
>   *	the platform's main firmware. If both this fallback and the sysfs
>   *      fallback are enabled, then this fallback will be tried first.
> + * @FW_OPT_PARTIAL: Allow partial read of firmware instead of needing to read
> + *	entire file.
>   */
>  enum fw_opt {
>  	FW_OPT_UEVENT			= BIT(0),
> @@ -41,6 +43,7 @@ enum fw_opt {
>  	FW_OPT_NOCACHE			= BIT(4),
>  	FW_OPT_NOFALLBACK_SYSFS		= BIT(5),
>  	FW_OPT_FALLBACK_PLATFORM	= BIT(6),
> +	FW_OPT_PARTIAL			= BIT(7),
>  };
>  
>  enum fw_status {
> @@ -68,6 +71,7 @@ struct fw_priv {
>  	void *data;
>  	size_t size;
>  	size_t allocated_size;
> +	size_t offset;
>  	u32 opt_flags;
>  #ifdef CONFIG_FW_LOADER_PAGED_BUF
>  	bool is_paged_buf;
> diff --git a/drivers/base/firmware_loader/main.c b/drivers/base/firmware_loader/main.c
> index 814a18cc51bd..7aa22bdc2f60 100644
> --- a/drivers/base/firmware_loader/main.c
> +++ b/drivers/base/firmware_loader/main.c
> @@ -170,10 +170,19 @@ static struct fw_priv *__allocate_fw_priv(const char *fw_name,
>  					  struct firmware_cache *fwc,
>  					  void *dbuf,
>  					  size_t size,
> +					  size_t offset,
>  					  u32 opt_flags)
>  {
>  	struct fw_priv *fw_priv;
>  
> +	/* For a partial read, the buffer must be preallocated. */
> +	if ((opt_flags & FW_OPT_PARTIAL) && !dbuf)
> +		return NULL;
> +
> +	/* Only partial reads are allowed to use an offset. */
> +	if (offset != 0 && !(opt_flags & FW_OPT_PARTIAL))
> +		return NULL;
> +
>  	fw_priv = kzalloc(sizeof(*fw_priv), GFP_ATOMIC);
>  	if (!fw_priv)
>  		return NULL;
> @@ -188,6 +197,7 @@ static struct fw_priv *__allocate_fw_priv(const char *fw_name,
>  	fw_priv->fwc = fwc;
>  	fw_priv->data = dbuf;
>  	fw_priv->allocated_size = size;
> +	fw_priv->offset = offset;
>  	fw_priv->opt_flags = opt_flags;
>  	fw_state_init(fw_priv);
>  #ifdef CONFIG_FW_LOADER_USER_HELPER
> @@ -216,12 +226,17 @@ static int alloc_lookup_fw_priv(const char *fw_name,
>  				struct fw_priv **fw_priv,
>  				void *dbuf,
>  				size_t size,
> +				size_t offset,
>  				u32 opt_flags)
>  {
>  	struct fw_priv *tmp;
>  
>  	spin_lock(&fwc->lock);
> -	if (!(opt_flags & FW_OPT_NOCACHE)) {
> +	/*
> +	 * Do not merge requests that are marked to be non-cached or
> +	 * are performing partial reads.
> +	 */
> +	if (!(opt_flags & (FW_OPT_NOCACHE | FW_OPT_PARTIAL))) {
>  		tmp = __lookup_fw_priv(fw_name);
>  		if (tmp) {
>  			kref_get(&tmp->ref);
> @@ -232,7 +247,7 @@ static int alloc_lookup_fw_priv(const char *fw_name,
>  		}
>  	}
>  
> -	tmp = __allocate_fw_priv(fw_name, fwc, dbuf, size, opt_flags);
> +	tmp = __allocate_fw_priv(fw_name, fwc, dbuf, size, offset, opt_flags);
>  	if (tmp) {
>  		INIT_LIST_HEAD(&tmp->list);
>  		if (!(opt_flags & FW_OPT_NOCACHE))
> @@ -439,6 +454,12 @@ static int fw_decompress_xz(struct device *dev, struct fw_priv *fw_priv,
>  	else
>  		return fw_decompress_xz_pages(dev, fw_priv, in_size, in_buffer);
>  }
> +#else
> +static inline int fw_decompress_xz(struct device *dev, struct fw_priv *fw_priv,
> +				   size_t in_size, const void *in_buffer)
> +{
> +	return -ENOENT;
> +}
>  #endif /* CONFIG_FW_LOADER_COMPRESS */
>  
>  /* direct firmware loading support */
> @@ -485,6 +506,9 @@ fw_get_filesystem_firmware(struct device *device, struct fw_priv *fw_priv,
>  		return -ENOMEM;
>  
>  	for (i = 0; i < ARRAY_SIZE(fw_path); i++) {
> +		size_t file_size = 0;
> +		size_t *file_size_ptr = NULL;
> +
>  		/* skip the unset customized path */
>  		if (!fw_path[i][0])
>  			continue;
> @@ -498,9 +522,18 @@ fw_get_filesystem_firmware(struct device *device, struct fw_priv *fw_priv,
>  
>  		fw_priv->size = 0;
>  
> +		/*
> +		 * The total file size is only examined when doing a partial
> +		 * read; the "full read" case needs to fail if the whole
> +		 * firmware was not completely loaded.
> +		 */
> +		if ((fw_priv->opt_flags & FW_OPT_PARTIAL) && buffer)
> +			file_size_ptr = &file_size;
> +
>  		/* load firmware files from the mount namespace of init */
> -		rc = kernel_read_file_from_path_initns(path, 0, &buffer, msize,
> -						       NULL,
> +		rc = kernel_read_file_from_path_initns(path, fw_priv->offset,
> +						       &buffer, msize,
> +						       file_size_ptr,
>  						       READING_FIRMWARE);
>  		if (rc < 0) {
>  			if (rc != -ENOENT)
> @@ -691,7 +724,7 @@ int assign_fw(struct firmware *fw, struct device *device)
>  static int
>  _request_firmware_prepare(struct firmware **firmware_p, const char *name,
>  			  struct device *device, void *dbuf, size_t size,
> -			  u32 opt_flags)
> +			  size_t offset, u32 opt_flags)
>  {
>  	struct firmware *firmware;
>  	struct fw_priv *fw_priv;
> @@ -710,7 +743,7 @@ _request_firmware_prepare(struct firmware **firmware_p, const char *name,
>  	}
>  
>  	ret = alloc_lookup_fw_priv(name, &fw_cache, &fw_priv, dbuf, size,
> -				  opt_flags);
> +				   offset, opt_flags);
>  
>  	/*
>  	 * bind with 'priv' now to avoid warning in failure path
> @@ -757,9 +790,10 @@ static void fw_abort_batch_reqs(struct firmware *fw)
>  static int
>  _request_firmware(const struct firmware **firmware_p, const char *name,
>  		  struct device *device, void *buf, size_t size,
> -		  u32 opt_flags)
> +		  size_t offset, u32 opt_flags)
>  {
>  	struct firmware *fw = NULL;
> +	bool nondirect = false;
>  	int ret;
>  
>  	if (!firmware_p)
> @@ -771,18 +805,20 @@ _request_firmware(const struct firmware **firmware_p, const char *name,
>  	}
>  
>  	ret = _request_firmware_prepare(&fw, name, device, buf, size,
> -					opt_flags);
> +					offset, opt_flags);
>  	if (ret <= 0) /* error or already assigned */
>  		goto out;
>  
>  	ret = fw_get_filesystem_firmware(device, fw->priv, "", NULL);
> -#ifdef CONFIG_FW_LOADER_COMPRESS
> -	if (ret == -ENOENT)
> +
> +	/* Only full reads can support decompression, platform, and sysfs. */
> +	if (!(opt_flags & FW_OPT_PARTIAL))
> +		nondirect = true;
> +
> +	if (ret == -ENOENT && nondirect)
>  		ret = fw_get_filesystem_firmware(device, fw->priv, ".xz",
>  						 fw_decompress_xz);
> -#endif
> -
> -	if (ret == -ENOENT)
> +	if (ret == -ENOENT && nondirect)
>  		ret = firmware_fallback_platform(fw->priv);
>  
>  	if (ret) {
> @@ -790,7 +826,9 @@ _request_firmware(const struct firmware **firmware_p, const char *name,
>  			dev_warn(device,
>  				 "Direct firmware load for %s failed with error %d\n",
>  				 name, ret);
> -		ret = firmware_fallback_sysfs(fw, name, device, opt_flags, ret);
> +		if (nondirect)
> +			ret = firmware_fallback_sysfs(fw, name, device,
> +						      opt_flags, ret);
>  	} else
>  		ret = assign_fw(fw, device);
>  
> @@ -833,7 +871,7 @@ request_firmware(const struct firmware **firmware_p, const char *name,
>  
>  	/* Need to pin this module until return */
>  	__module_get(THIS_MODULE);
> -	ret = _request_firmware(firmware_p, name, device, NULL, 0,
> +	ret = _request_firmware(firmware_p, name, device, NULL, 0, 0,
>  				FW_OPT_UEVENT);
>  	module_put(THIS_MODULE);
>  	return ret;
> @@ -860,7 +898,7 @@ int firmware_request_nowarn(const struct firmware **firmware, const char *name,
>  
>  	/* Need to pin this module until return */
>  	__module_get(THIS_MODULE);
> -	ret = _request_firmware(firmware, name, device, NULL, 0,
> +	ret = _request_firmware(firmware, name, device, NULL, 0, 0,
>  				FW_OPT_UEVENT | FW_OPT_NO_WARN);
>  	module_put(THIS_MODULE);
>  	return ret;
> @@ -884,7 +922,7 @@ int request_firmware_direct(const struct firmware **firmware_p,
>  	int ret;
>  
>  	__module_get(THIS_MODULE);
> -	ret = _request_firmware(firmware_p, name, device, NULL, 0,
> +	ret = _request_firmware(firmware_p, name, device, NULL, 0, 0,
>  				FW_OPT_UEVENT | FW_OPT_NO_WARN |
>  				FW_OPT_NOFALLBACK_SYSFS);
>  	module_put(THIS_MODULE);
> @@ -909,7 +947,7 @@ int firmware_request_platform(const struct firmware **firmware,
>  
>  	/* Need to pin this module until return */
>  	__module_get(THIS_MODULE);
> -	ret = _request_firmware(firmware, name, device, NULL, 0,
> +	ret = _request_firmware(firmware, name, device, NULL, 0, 0,
>  				FW_OPT_UEVENT | FW_OPT_FALLBACK_PLATFORM);
>  	module_put(THIS_MODULE);
>  	return ret;
> @@ -965,13 +1003,44 @@ request_firmware_into_buf(const struct firmware **firmware_p, const char *name,
>  		return -EOPNOTSUPP;
>  
>  	__module_get(THIS_MODULE);
> -	ret = _request_firmware(firmware_p, name, device, buf, size,
> +	ret = _request_firmware(firmware_p, name, device, buf, size, 0,
>  				FW_OPT_UEVENT | FW_OPT_NOCACHE);
>  	module_put(THIS_MODULE);
>  	return ret;
>  }
>  EXPORT_SYMBOL(request_firmware_into_buf);
>  
> +/**
> + * request_partial_firmware_into_buf() - load partial firmware into a previously allocated buffer
> + * @firmware_p: pointer to firmware image
> + * @name: name of firmware file
> + * @device: device for which firmware is being loaded and DMA region allocated
> + * @buf: address of buffer to load firmware into
> + * @size: size of buffer
> + * @offset: offset into file to read
> + *
> + * This function works pretty much like request_firmware_into_buf except
> + * it allows a partial read of the file.
> + */
> +int
> +request_partial_firmware_into_buf(const struct firmware **firmware_p,
> +				  const char *name, struct device *device,
> +				  void *buf, size_t size, size_t offset)
> +{
> +	int ret;
> +
> +	if (fw_cache_is_setup(device, name))
> +		return -EOPNOTSUPP;
> +
> +	__module_get(THIS_MODULE);
> +	ret = _request_firmware(firmware_p, name, device, buf, size, offset,
> +				FW_OPT_UEVENT | FW_OPT_NOCACHE |
> +				FW_OPT_PARTIAL);
> +	module_put(THIS_MODULE);
> +	return ret;
> +}
> +EXPORT_SYMBOL(request_partial_firmware_into_buf);
> +
>  /**
>   * release_firmware() - release the resource associated with a firmware image
>   * @fw: firmware resource to release
> @@ -1004,7 +1073,7 @@ static void request_firmware_work_func(struct work_struct *work)
>  
>  	fw_work = container_of(work, struct firmware_work, work);
>  
> -	_request_firmware(&fw, fw_work->name, fw_work->device, NULL, 0,
> +	_request_firmware(&fw, fw_work->name, fw_work->device, NULL, 0, 0,
>  			  fw_work->opt_flags);
>  	fw_work->cont(fw, fw_work->context);
>  	put_device(fw_work->device); /* taken in request_firmware_nowait() */
> diff --git a/include/linux/firmware.h b/include/linux/firmware.h
> index cb3e2c06ed8a..c15acadc6cf4 100644
> --- a/include/linux/firmware.h
> +++ b/include/linux/firmware.h
> @@ -53,6 +53,9 @@ int request_firmware_direct(const struct firmware **fw, const char *name,
>  			    struct device *device);
>  int request_firmware_into_buf(const struct firmware **firmware_p,
>  	const char *name, struct device *device, void *buf, size_t size);
> +int request_partial_firmware_into_buf(const struct firmware **firmware_p,
> +				      const char *name, struct device *device,
> +				      void *buf, size_t size, size_t offset);
>  
>  void release_firmware(const struct firmware *fw);
>  #else
> @@ -102,6 +105,15 @@ static inline int request_firmware_into_buf(const struct firmware **firmware_p,
>  	return -EINVAL;
>  }
>  
> +static inline int request_partial_firmware_into_buf
> +					(const struct firmware **firmware_p,
> +					 const char *name,
> +					 struct device *device,
> +					 void *buf, size_t size, size_t offset)
> +{
> +	return -EINVAL;
> +}
> +
>  #endif
>  
>  int firmware_request_cache(struct device *device, const char *name);
> -- 
> 2.25.1
>
Takashi Iwai July 29, 2020, 6:22 a.m. UTC | #2
On Wed, 29 Jul 2020 03:17:39 +0200,
Luis Chamberlain wrote:
> 
> Long ago Takashi had some points about this strategy breaking
> compressed file use. Was that considered?

As long as I read the patch, it tries to skip both the compressed and
the fallback loading when FW_OPT_PARTIAL is set, which is good.

However...

> > @@ -771,18 +805,20 @@ _request_firmware(const struct firmware **firmware_p, const char *name,
> >  	}
> >  
> >  	ret = _request_firmware_prepare(&fw, name, device, buf, size,
> > -					opt_flags);
> > +					offset, opt_flags);
> >  	if (ret <= 0) /* error or already assigned */
> >  		goto out;
> >  
> >  	ret = fw_get_filesystem_firmware(device, fw->priv, "", NULL);
> > -#ifdef CONFIG_FW_LOADER_COMPRESS
> > -	if (ret == -ENOENT)
> > +
> > +	/* Only full reads can support decompression, platform, and sysfs. */
> > +	if (!(opt_flags & FW_OPT_PARTIAL))
> > +		nondirect = true;
> > +
> > +	if (ret == -ENOENT && nondirect)
> >  		ret = fw_get_filesystem_firmware(device, fw->priv, ".xz",
> >  						 fw_decompress_xz);
> > -#endif

... by dropping this ifdef, the fw loader would try to access *.xz
file unnecessarily even if CONFIG_FW_LOADER_COMPRESS is disabled.


thanks,

Takashi
Kees Cook July 29, 2020, 5:43 p.m. UTC | #3
On Wed, Jul 29, 2020 at 08:22:17AM +0200, Takashi Iwai wrote:
> On Wed, 29 Jul 2020 03:17:39 +0200,
> Luis Chamberlain wrote:
> > 
> > Long ago Takashi had some points about this strategy breaking
> > compressed file use. Was that considered?
> 
> As long as I read the patch, it tries to skip both the compressed and
> the fallback loading when FW_OPT_PARTIAL is set, which is good.
> 
> However...
> 
> > > @@ -771,18 +805,20 @@ _request_firmware(const struct firmware **firmware_p, const char *name,
> > >  	}
> > >  
> > >  	ret = _request_firmware_prepare(&fw, name, device, buf, size,
> > > -					opt_flags);
> > > +					offset, opt_flags);
> > >  	if (ret <= 0) /* error or already assigned */
> > >  		goto out;
> > >  
> > >  	ret = fw_get_filesystem_firmware(device, fw->priv, "", NULL);
> > > -#ifdef CONFIG_FW_LOADER_COMPRESS
> > > -	if (ret == -ENOENT)
> > > +
> > > +	/* Only full reads can support decompression, platform, and sysfs. */
> > > +	if (!(opt_flags & FW_OPT_PARTIAL))
> > > +		nondirect = true;
> > > +
> > > +	if (ret == -ENOENT && nondirect)
> > >  		ret = fw_get_filesystem_firmware(device, fw->priv, ".xz",
> > >  						 fw_decompress_xz);
> > > -#endif
> 
> ... by dropping this ifdef, the fw loader would try to access *.xz
> file unnecessarily even if CONFIG_FW_LOADER_COMPRESS is disabled.

Ah, good point. I'd added the -ENOENT fw_decompress_xz, but I take your
point about the needless access. I will switch this back to an #ifdef.

Patch
diff mbox series

diff --git a/drivers/base/firmware_loader/firmware.h b/drivers/base/firmware_loader/firmware.h
index 7ad5fe52bc72..3f6eda46b3a2 100644
--- a/drivers/base/firmware_loader/firmware.h
+++ b/drivers/base/firmware_loader/firmware.h
@@ -32,6 +32,8 @@ 
  * @FW_OPT_FALLBACK_PLATFORM: Enable fallback to device fw copy embedded in
  *	the platform's main firmware. If both this fallback and the sysfs
  *      fallback are enabled, then this fallback will be tried first.
+ * @FW_OPT_PARTIAL: Allow partial read of firmware instead of needing to read
+ *	entire file.
  */
 enum fw_opt {
 	FW_OPT_UEVENT			= BIT(0),
@@ -41,6 +43,7 @@  enum fw_opt {
 	FW_OPT_NOCACHE			= BIT(4),
 	FW_OPT_NOFALLBACK_SYSFS		= BIT(5),
 	FW_OPT_FALLBACK_PLATFORM	= BIT(6),
+	FW_OPT_PARTIAL			= BIT(7),
 };
 
 enum fw_status {
@@ -68,6 +71,7 @@  struct fw_priv {
 	void *data;
 	size_t size;
 	size_t allocated_size;
+	size_t offset;
 	u32 opt_flags;
 #ifdef CONFIG_FW_LOADER_PAGED_BUF
 	bool is_paged_buf;
diff --git a/drivers/base/firmware_loader/main.c b/drivers/base/firmware_loader/main.c
index 814a18cc51bd..7aa22bdc2f60 100644
--- a/drivers/base/firmware_loader/main.c
+++ b/drivers/base/firmware_loader/main.c
@@ -170,10 +170,19 @@  static struct fw_priv *__allocate_fw_priv(const char *fw_name,
 					  struct firmware_cache *fwc,
 					  void *dbuf,
 					  size_t size,
+					  size_t offset,
 					  u32 opt_flags)
 {
 	struct fw_priv *fw_priv;
 
+	/* For a partial read, the buffer must be preallocated. */
+	if ((opt_flags & FW_OPT_PARTIAL) && !dbuf)
+		return NULL;
+
+	/* Only partial reads are allowed to use an offset. */
+	if (offset != 0 && !(opt_flags & FW_OPT_PARTIAL))
+		return NULL;
+
 	fw_priv = kzalloc(sizeof(*fw_priv), GFP_ATOMIC);
 	if (!fw_priv)
 		return NULL;
@@ -188,6 +197,7 @@  static struct fw_priv *__allocate_fw_priv(const char *fw_name,
 	fw_priv->fwc = fwc;
 	fw_priv->data = dbuf;
 	fw_priv->allocated_size = size;
+	fw_priv->offset = offset;
 	fw_priv->opt_flags = opt_flags;
 	fw_state_init(fw_priv);
 #ifdef CONFIG_FW_LOADER_USER_HELPER
@@ -216,12 +226,17 @@  static int alloc_lookup_fw_priv(const char *fw_name,
 				struct fw_priv **fw_priv,
 				void *dbuf,
 				size_t size,
+				size_t offset,
 				u32 opt_flags)
 {
 	struct fw_priv *tmp;
 
 	spin_lock(&fwc->lock);
-	if (!(opt_flags & FW_OPT_NOCACHE)) {
+	/*
+	 * Do not merge requests that are marked to be non-cached or
+	 * are performing partial reads.
+	 */
+	if (!(opt_flags & (FW_OPT_NOCACHE | FW_OPT_PARTIAL))) {
 		tmp = __lookup_fw_priv(fw_name);
 		if (tmp) {
 			kref_get(&tmp->ref);
@@ -232,7 +247,7 @@  static int alloc_lookup_fw_priv(const char *fw_name,
 		}
 	}
 
-	tmp = __allocate_fw_priv(fw_name, fwc, dbuf, size, opt_flags);
+	tmp = __allocate_fw_priv(fw_name, fwc, dbuf, size, offset, opt_flags);
 	if (tmp) {
 		INIT_LIST_HEAD(&tmp->list);
 		if (!(opt_flags & FW_OPT_NOCACHE))
@@ -439,6 +454,12 @@  static int fw_decompress_xz(struct device *dev, struct fw_priv *fw_priv,
 	else
 		return fw_decompress_xz_pages(dev, fw_priv, in_size, in_buffer);
 }
+#else
+static inline int fw_decompress_xz(struct device *dev, struct fw_priv *fw_priv,
+				   size_t in_size, const void *in_buffer)
+{
+	return -ENOENT;
+}
 #endif /* CONFIG_FW_LOADER_COMPRESS */
 
 /* direct firmware loading support */
@@ -485,6 +506,9 @@  fw_get_filesystem_firmware(struct device *device, struct fw_priv *fw_priv,
 		return -ENOMEM;
 
 	for (i = 0; i < ARRAY_SIZE(fw_path); i++) {
+		size_t file_size = 0;
+		size_t *file_size_ptr = NULL;
+
 		/* skip the unset customized path */
 		if (!fw_path[i][0])
 			continue;
@@ -498,9 +522,18 @@  fw_get_filesystem_firmware(struct device *device, struct fw_priv *fw_priv,
 
 		fw_priv->size = 0;
 
+		/*
+		 * The total file size is only examined when doing a partial
+		 * read; the "full read" case needs to fail if the whole
+		 * firmware was not completely loaded.
+		 */
+		if ((fw_priv->opt_flags & FW_OPT_PARTIAL) && buffer)
+			file_size_ptr = &file_size;
+
 		/* load firmware files from the mount namespace of init */
-		rc = kernel_read_file_from_path_initns(path, 0, &buffer, msize,
-						       NULL,
+		rc = kernel_read_file_from_path_initns(path, fw_priv->offset,
+						       &buffer, msize,
+						       file_size_ptr,
 						       READING_FIRMWARE);
 		if (rc < 0) {
 			if (rc != -ENOENT)
@@ -691,7 +724,7 @@  int assign_fw(struct firmware *fw, struct device *device)
 static int
 _request_firmware_prepare(struct firmware **firmware_p, const char *name,
 			  struct device *device, void *dbuf, size_t size,
-			  u32 opt_flags)
+			  size_t offset, u32 opt_flags)
 {
 	struct firmware *firmware;
 	struct fw_priv *fw_priv;
@@ -710,7 +743,7 @@  _request_firmware_prepare(struct firmware **firmware_p, const char *name,
 	}
 
 	ret = alloc_lookup_fw_priv(name, &fw_cache, &fw_priv, dbuf, size,
-				  opt_flags);
+				   offset, opt_flags);
 
 	/*
 	 * bind with 'priv' now to avoid warning in failure path
@@ -757,9 +790,10 @@  static void fw_abort_batch_reqs(struct firmware *fw)
 static int
 _request_firmware(const struct firmware **firmware_p, const char *name,
 		  struct device *device, void *buf, size_t size,
-		  u32 opt_flags)
+		  size_t offset, u32 opt_flags)
 {
 	struct firmware *fw = NULL;
+	bool nondirect = false;
 	int ret;
 
 	if (!firmware_p)
@@ -771,18 +805,20 @@  _request_firmware(const struct firmware **firmware_p, const char *name,
 	}
 
 	ret = _request_firmware_prepare(&fw, name, device, buf, size,
-					opt_flags);
+					offset, opt_flags);
 	if (ret <= 0) /* error or already assigned */
 		goto out;
 
 	ret = fw_get_filesystem_firmware(device, fw->priv, "", NULL);
-#ifdef CONFIG_FW_LOADER_COMPRESS
-	if (ret == -ENOENT)
+
+	/* Only full reads can support decompression, platform, and sysfs. */
+	if (!(opt_flags & FW_OPT_PARTIAL))
+		nondirect = true;
+
+	if (ret == -ENOENT && nondirect)
 		ret = fw_get_filesystem_firmware(device, fw->priv, ".xz",
 						 fw_decompress_xz);
-#endif
-
-	if (ret == -ENOENT)
+	if (ret == -ENOENT && nondirect)
 		ret = firmware_fallback_platform(fw->priv);
 
 	if (ret) {
@@ -790,7 +826,9 @@  _request_firmware(const struct firmware **firmware_p, const char *name,
 			dev_warn(device,
 				 "Direct firmware load for %s failed with error %d\n",
 				 name, ret);
-		ret = firmware_fallback_sysfs(fw, name, device, opt_flags, ret);
+		if (nondirect)
+			ret = firmware_fallback_sysfs(fw, name, device,
+						      opt_flags, ret);
 	} else
 		ret = assign_fw(fw, device);
 
@@ -833,7 +871,7 @@  request_firmware(const struct firmware **firmware_p, const char *name,
 
 	/* Need to pin this module until return */
 	__module_get(THIS_MODULE);
-	ret = _request_firmware(firmware_p, name, device, NULL, 0,
+	ret = _request_firmware(firmware_p, name, device, NULL, 0, 0,
 				FW_OPT_UEVENT);
 	module_put(THIS_MODULE);
 	return ret;
@@ -860,7 +898,7 @@  int firmware_request_nowarn(const struct firmware **firmware, const char *name,
 
 	/* Need to pin this module until return */
 	__module_get(THIS_MODULE);
-	ret = _request_firmware(firmware, name, device, NULL, 0,
+	ret = _request_firmware(firmware, name, device, NULL, 0, 0,
 				FW_OPT_UEVENT | FW_OPT_NO_WARN);
 	module_put(THIS_MODULE);
 	return ret;
@@ -884,7 +922,7 @@  int request_firmware_direct(const struct firmware **firmware_p,
 	int ret;
 
 	__module_get(THIS_MODULE);
-	ret = _request_firmware(firmware_p, name, device, NULL, 0,
+	ret = _request_firmware(firmware_p, name, device, NULL, 0, 0,
 				FW_OPT_UEVENT | FW_OPT_NO_WARN |
 				FW_OPT_NOFALLBACK_SYSFS);
 	module_put(THIS_MODULE);
@@ -909,7 +947,7 @@  int firmware_request_platform(const struct firmware **firmware,
 
 	/* Need to pin this module until return */
 	__module_get(THIS_MODULE);
-	ret = _request_firmware(firmware, name, device, NULL, 0,
+	ret = _request_firmware(firmware, name, device, NULL, 0, 0,
 				FW_OPT_UEVENT | FW_OPT_FALLBACK_PLATFORM);
 	module_put(THIS_MODULE);
 	return ret;
@@ -965,13 +1003,44 @@  request_firmware_into_buf(const struct firmware **firmware_p, const char *name,
 		return -EOPNOTSUPP;
 
 	__module_get(THIS_MODULE);
-	ret = _request_firmware(firmware_p, name, device, buf, size,
+	ret = _request_firmware(firmware_p, name, device, buf, size, 0,
 				FW_OPT_UEVENT | FW_OPT_NOCACHE);
 	module_put(THIS_MODULE);
 	return ret;
 }
 EXPORT_SYMBOL(request_firmware_into_buf);
 
+/**
+ * request_partial_firmware_into_buf() - load partial firmware into a previously allocated buffer
+ * @firmware_p: pointer to firmware image
+ * @name: name of firmware file
+ * @device: device for which firmware is being loaded and DMA region allocated
+ * @buf: address of buffer to load firmware into
+ * @size: size of buffer
+ * @offset: offset into file to read
+ *
+ * This function works pretty much like request_firmware_into_buf except
+ * it allows a partial read of the file.
+ */
+int
+request_partial_firmware_into_buf(const struct firmware **firmware_p,
+				  const char *name, struct device *device,
+				  void *buf, size_t size, size_t offset)
+{
+	int ret;
+
+	if (fw_cache_is_setup(device, name))
+		return -EOPNOTSUPP;
+
+	__module_get(THIS_MODULE);
+	ret = _request_firmware(firmware_p, name, device, buf, size, offset,
+				FW_OPT_UEVENT | FW_OPT_NOCACHE |
+				FW_OPT_PARTIAL);
+	module_put(THIS_MODULE);
+	return ret;
+}
+EXPORT_SYMBOL(request_partial_firmware_into_buf);
+
 /**
  * release_firmware() - release the resource associated with a firmware image
  * @fw: firmware resource to release
@@ -1004,7 +1073,7 @@  static void request_firmware_work_func(struct work_struct *work)
 
 	fw_work = container_of(work, struct firmware_work, work);
 
-	_request_firmware(&fw, fw_work->name, fw_work->device, NULL, 0,
+	_request_firmware(&fw, fw_work->name, fw_work->device, NULL, 0, 0,
 			  fw_work->opt_flags);
 	fw_work->cont(fw, fw_work->context);
 	put_device(fw_work->device); /* taken in request_firmware_nowait() */
diff --git a/include/linux/firmware.h b/include/linux/firmware.h
index cb3e2c06ed8a..c15acadc6cf4 100644
--- a/include/linux/firmware.h
+++ b/include/linux/firmware.h
@@ -53,6 +53,9 @@  int request_firmware_direct(const struct firmware **fw, const char *name,
 			    struct device *device);
 int request_firmware_into_buf(const struct firmware **firmware_p,
 	const char *name, struct device *device, void *buf, size_t size);
+int request_partial_firmware_into_buf(const struct firmware **firmware_p,
+				      const char *name, struct device *device,
+				      void *buf, size_t size, size_t offset);
 
 void release_firmware(const struct firmware *fw);
 #else
@@ -102,6 +105,15 @@  static inline int request_firmware_into_buf(const struct firmware **firmware_p,
 	return -EINVAL;
 }
 
+static inline int request_partial_firmware_into_buf
+					(const struct firmware **firmware_p,
+					 const char *name,
+					 struct device *device,
+					 void *buf, size_t size, size_t offset)
+{
+	return -EINVAL;
+}
+
 #endif
 
 int firmware_request_cache(struct device *device, const char *name);