[PATCH] virtio: add support for SIZE_MAX & SEG_MAX features

[PATCH] virtio: add support for SIZE_MAX & SEG_MAX features

[Christian Pötzsch]

Some virtio implementations may forward the virtio requests directly to
the underlying hw. The hw may have some restrictions in how many and how
big the requests can be. Therefore, the corresponding virtio device will
announce this limitations with the SIZE_MAX & SEG_MAX feature.

Add support for those features. Split an io request into multiple virtio
requests if more than seg_max segments would be used. Also split a
single buffer request into multiple segments if the buffer is bigger
then size_max.

Signed-off-by: Christian Pötzsch <christian.poetzsch@kernkonzept.com>
Signed-off-by: Adam Lackorzynski <adam@l4re.org>
---
 drivers/virtio/virtio_blk.c | 110 ++++++++++++++++++++++++++++--------
 1 file changed, 88 insertions(+), 22 deletions(-)

diff --git a/drivers/virtio/virtio_blk.c b/drivers/virtio/virtio_blk.c
index 3dd0cf36268..80006a49e4a 100644
--- a/drivers/virtio/virtio_blk.c
+++ b/drivers/virtio/virtio_blk.c
@@ -14,6 +14,7 @@
 #include <virtio_ring.h>
 #include <linux/log2.h>
 #include "virtio_blk.h"
+#include <malloc.h>
 
 /**
  * struct virtio_blk_priv - private data for virtio block device
@@ -23,10 +24,16 @@ struct virtio_blk_priv {
 	struct virtqueue *vq;
 	/** @blksz_shift - log2 of block size divided by 512 */
 	u32 blksz_shift;
+	/** @size_max - maximum segment size */
+	u32 size_max;
+	/** @seg_max - maximum segment count */
+	u32 seg_max;
 };
 
 static const u32 feature[] = {
 	VIRTIO_BLK_F_BLK_SIZE,
+	VIRTIO_BLK_F_SIZE_MAX,
+	VIRTIO_BLK_F_SEG_MAX,
 	VIRTIO_BLK_F_WRITE_ZEROES
 };
 
@@ -67,50 +74,69 @@ static void virtio_blk_init_data_sg(void *buffer, lbaint_t blkcnt, struct virtio
 	sg->length = blkcnt * 512;
 }
 
-static ulong virtio_blk_do_req(struct udevice *dev, u64 sector,
-			       lbaint_t blkcnt, void *buffer, u32 type)
+static ulong virtio_blk_do_single_req(struct udevice *dev, u64 sector,
+				      lbaint_t blkcnt, char *buffer, u32 type)
 {
 	struct virtio_blk_priv *priv = dev_get_priv(dev);
+	// The virtio device may have constrains on the maximum segment size.
+	// Calculate how many segments we need.
+	u32 seg_cnt = (blkcnt * 512) / priv->size_max + 1;
+	lbaint_t seg_sec_cnt = priv->size_max / 512;
 	struct virtio_blk_outhdr out_hdr;
 	struct virtio_blk_discard_write_zeroes wz_hdr;
 	unsigned int num_out = 0, num_in = 0;
-	struct virtio_sg hdr_sg, wz_sg, data_sg, status_sg;
-	struct virtio_sg *sgs[3];
+	struct virtio_sg **sgs;
 	u8 status;
 	int ret;
+	u32 i;
+
+	// +2 is header and status descriptor; seg_cnt is the number of data segments
+	// required. Needs to be dynamically allocated.
+	sgs = calloc(seg_cnt + 2, sizeof(struct virtio_sg *));
+	if (!sgs)
+		return -ENOMEM;
+
+	for (i = 0; i < seg_cnt + 2; ++i) {
+		sgs[i] = malloc(sizeof(struct virtio_sg));
+		if (!sgs[i])
+			goto err_free;
+	}
 
-	sector <<= priv->blksz_shift;
-	blkcnt <<= priv->blksz_shift;
-	virtio_blk_init_header_sg(dev, sector, type, &out_hdr, &hdr_sg);
-	sgs[num_out++] = &hdr_sg;
+	virtio_blk_init_header_sg(dev, sector, type, &out_hdr, sgs[num_out++]);
 
 	switch (type) {
 	case VIRTIO_BLK_T_IN:
-	case VIRTIO_BLK_T_OUT:
-		virtio_blk_init_data_sg(buffer, blkcnt, &data_sg);
-		if (type & VIRTIO_BLK_T_OUT)
-			sgs[num_out++] = &data_sg;
-		else
-			sgs[num_out + num_in++] = &data_sg;
+	case VIRTIO_BLK_T_OUT: {
+		i = 0;
+		while (i < blkcnt) {
+			u32 blk_per_seg = min(blkcnt - i, seg_sec_cnt);
+
+			if (type & VIRTIO_BLK_T_OUT)
+				virtio_blk_init_data_sg(buffer + i * 512, blk_per_seg,
+							sgs[num_out++]);
+			else
+				virtio_blk_init_data_sg(buffer + i * 512, blk_per_seg,
+							sgs[num_out + num_in++]);
+			i += blk_per_seg;
+		}
 		break;
-
+	}
 	case VIRTIO_BLK_T_WRITE_ZEROES:
-		virtio_blk_init_write_zeroes_sg(dev, sector, blkcnt, &wz_hdr, &wz_sg);
-		sgs[num_out++] = &wz_sg;
+		virtio_blk_init_write_zeroes_sg(dev, sector, blkcnt, &wz_hdr,
+						sgs[num_out++]);
 		break;
 
 	default:
-		return -EINVAL;
+		goto err_free;
 	}
 
-	virtio_blk_init_status_sg(&status, &status_sg);
-	sgs[num_out + num_in++] = &status_sg;
+	virtio_blk_init_status_sg(&status, sgs[num_out + num_in++]);
 	log_debug("dev=%s, active=%d, priv=%p, priv->vq=%p\n", dev->name,
 		  device_active(dev), priv, priv->vq);
 
 	ret = virtqueue_add(priv->vq, sgs, num_out, num_in);
 	if (ret)
-		return ret;
+		goto err_free;
 
 	virtqueue_kick(priv->vq);
 
@@ -119,7 +145,38 @@ static ulong virtio_blk_do_req(struct udevice *dev, u64 sector,
 		;
 	log_debug("done\n");
 
-	return status == VIRTIO_BLK_S_OK ? blkcnt >> priv->blksz_shift : -EIO;
+err_free:
+	for (i = 0; i < seg_cnt + 2; ++i)
+		free(sgs[i]);
+	free(sgs);
+
+	return status == VIRTIO_BLK_S_OK ? blkcnt : -EIO;
+}
+
+static ulong virtio_blk_do_req(struct udevice *dev, u64 sector,
+			       lbaint_t blkcnt, char *buffer, u32 type)
+{
+	struct virtio_blk_priv *priv = dev_get_priv(dev);
+	lbaint_t seg_sec_cnt = priv->size_max / 512;
+	u32 i = 0;
+	ulong ret;
+
+	sector <<= priv->blksz_shift;
+	blkcnt <<= priv->blksz_shift;
+
+	// The virtio device may have constrains on the maximum segment count. So
+	// send multiple virtio requests one after each other, if so.
+	while (i < blkcnt) {
+		u32 blk_per_sg = min(blkcnt - i, seg_sec_cnt * priv->seg_max);
+
+		ret = virtio_blk_do_single_req(dev, sector + i, blk_per_sg,
+					       buffer + i * 512, type);
+		if (!ret)
+			return ret;
+		i += blk_per_sg;
+	}
+
+	return blkcnt >> priv->blksz_shift;
 }
 
 static ulong virtio_blk_read(struct udevice *dev, lbaint_t start,
@@ -207,6 +264,15 @@ static int virtio_blk_probe(struct udevice *dev)
 	priv->blksz_shift = desc->log2blksz - 9;
 	desc->lba >>= priv->blksz_shift;
 
+	if (virtio_has_feature(dev, VIRTIO_BLK_F_SIZE_MAX))
+		virtio_cread(dev, struct virtio_blk_config, size_max, &priv->size_max);
+	else
+		priv->size_max = -1U;
+	if (virtio_has_feature(dev, VIRTIO_BLK_F_SEG_MAX))
+		virtio_cread(dev, struct virtio_blk_config, seg_max, &priv->seg_max);
+	else
+		priv->seg_max = -1U;
+
 	return 0;
 }
 
-- 
2.47.3

Re: [PATCH] virtio: add support for SIZE_MAX & SEG_MAX features

[Simon Glass]

Hi Christian,

On 2026-03-27T08:18:58, Christian Pötzsch
<christian.poetzsch@kernkonzept.com> wrote:
> virtio: add support for SIZE_MAX & SEG_MAX features
> virtio: add support for SIZE_MAX & SEG_MAX features
>
> Some virtio implementations may forward the virtio requests directly to
> the underlying hw. The hw may have some restrictions in how many and how
> big the requests can be. Therefore, the corresponding virtio device will
> announce this limitations with the SIZE_MAX & SEG_MAX feature.
>
> Add support for those features. Split an io request into multiple virtio
> requests if more than seg_max segments would be used. Also split a
> single buffer request into multiple segments if the buffer is bigger
> then size_max.
>
> Signed-off-by: Christian Pötzsch <christian.poetzsch@kernkonzept.com>
> Signed-off-by: Adam Lackorzynski <adam@l4re.org>

> diff --git a/drivers/virtio/virtio_blk.c b/drivers/virtio/virtio_blk.c
> @@ -119,7 +145,38 @@ static ulong virtio_blk_do_req(...)
> +err_free:
> +     for (i = 0; i < seg_cnt + 2; ++i)
> +             free(sgs[i]);
> +     free(sgs);
> +
> +     return status == VIRTIO_BLK_S_OK ? blkcnt : -EIO;

The err_free label is reached from both the success path (fall-through
after virtqueue_get_buf()) and error paths (goto from malloc()
failure, virtqueue_add() failure, or unknown type). On error paths,
status is uninitialised, so the final check has undefined behaviour.
Please can you separate the success path from the error cleanup, e.g.
with an explicit return before the err_free label.

> diff --git a/drivers/virtio/virtio_blk.c b/drivers/virtio/virtio_blk.c
> @@ -145,38 +145,38 @@ static ulong virtio_blk_do_req(...)
> +     while (i < blkcnt) {
> +             u32 blk_per_sg = min(blkcnt - i, seg_sec_cnt * priv->seg_max);
> +
> +             ret = virtio_blk_do_single_req(dev, sector + i, blk_per_sg,
> +                                            buffer + i * 512, type);
> +             if (!ret)
> +                     return ret;

The error check is inverted. virtio_blk_do_single_req() returns blkcnt
(positive) on success and -EIO on failure, so if (!ret) only triggers
when ret is zero. I suspect you want if (ret < 0) here.

BTW please add a function comment for virtio_blk_do_single_req() so
all this is clearer.

> diff --git a/drivers/virtio/virtio_blk.c b/drivers/virtio/virtio_blk.c
> @@ -67,50 +74,69 @@ static void virtio_blk_init_data_sg(...)
> +     // The virtio device may have constrains on the maximum segment size.

U-Boot follows the Linux kernel coding style which prefers /* */
comments over //. Please can you convert these.

Regards,
Simon

Re: [PATCH] virtio: add support for SIZE_MAX & SEG_MAX features

[Tom Rini]

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On Thu, Apr 02, 2026 at 01:41:11PM -0600, Simon Glass wrote:
> Hi Christian,
> 
> On 2026-03-27T08:18:58, Christian Pötzsch
> <christian.poetzsch@kernkonzept.com> wrote:
> > virtio: add support for SIZE_MAX & SEG_MAX features
> > virtio: add support for SIZE_MAX & SEG_MAX features
> >
> > Some virtio implementations may forward the virtio requests directly to
> > the underlying hw. The hw may have some restrictions in how many and how
> > big the requests can be. Therefore, the corresponding virtio device will
> > announce this limitations with the SIZE_MAX & SEG_MAX feature.
> >
> > Add support for those features. Split an io request into multiple virtio
> > requests if more than seg_max segments would be used. Also split a
> > single buffer request into multiple segments if the buffer is bigger
> > then size_max.
> >
> > Signed-off-by: Christian Pötzsch <christian.poetzsch@kernkonzept.com>
> > Signed-off-by: Adam Lackorzynski <adam@l4re.org>
> 
> > diff --git a/drivers/virtio/virtio_blk.c b/drivers/virtio/virtio_blk.c
> > @@ -119,7 +145,38 @@ static ulong virtio_blk_do_req(...)
> > +err_free:
> > +     for (i = 0; i < seg_cnt + 2; ++i)
> > +             free(sgs[i]);
> > +     free(sgs);
> > +
> > +     return status == VIRTIO_BLK_S_OK ? blkcnt : -EIO;
> 
> The err_free label is reached from both the success path (fall-through
> after virtqueue_get_buf()) and error paths (goto from malloc()
> failure, virtqueue_add() failure, or unknown type). On error paths,
> status is uninitialised, so the final check has undefined behaviour.
> Please can you separate the success path from the error cleanup, e.g.
> with an explicit return before the err_free label.
> 
> > diff --git a/drivers/virtio/virtio_blk.c b/drivers/virtio/virtio_blk.c
> > @@ -145,38 +145,38 @@ static ulong virtio_blk_do_req(...)
> > +     while (i < blkcnt) {
> > +             u32 blk_per_sg = min(blkcnt - i, seg_sec_cnt * priv->seg_max);
> > +
> > +             ret = virtio_blk_do_single_req(dev, sector + i, blk_per_sg,
> > +                                            buffer + i * 512, type);
> > +             if (!ret)
> > +                     return ret;
> 
> The error check is inverted. virtio_blk_do_single_req() returns blkcnt
> (positive) on success and -EIO on failure, so if (!ret) only triggers
> when ret is zero. I suspect you want if (ret < 0) here.
> 
> BTW please add a function comment for virtio_blk_do_single_req() so
> all this is clearer.

This is all true, and useful feedback.

> > diff --git a/drivers/virtio/virtio_blk.c b/drivers/virtio/virtio_blk.c
> > @@ -67,50 +74,69 @@ static void virtio_blk_init_data_sg(...)
> > +     // The virtio device may have constrains on the maximum segment size.
> 
> U-Boot follows the Linux kernel coding style which prefers /* */
> comments over //. Please can you convert these.

This hasn't been true for a number of years, Linux Kernel nor here.
We've accepted C99-style comments (when not needing to be kernel-doc)
for a long time now.

-- 
Tom

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Re: [PATCH] virtio: add support for SIZE_MAX & SEG_MAX features

[Christian Pötzsch]

Hi all,

On 4/8/26 9:12 PM, Tom Rini wrote:
> On Thu, Apr 02, 2026 at 01:41:11PM -0600, Simon Glass wrote:
>> Hi Christian,
>>
>> On 2026-03-27T08:18:58, Christian Pötzsch
>> <christian.poetzsch@kernkonzept.com> wrote:
>>> virtio: add support for SIZE_MAX & SEG_MAX features
>>> virtio: add support for SIZE_MAX & SEG_MAX features
>>>
>>> Some virtio implementations may forward the virtio requests directly to
>>> the underlying hw. The hw may have some restrictions in how many and how
>>> big the requests can be. Therefore, the corresponding virtio device will
>>> announce this limitations with the SIZE_MAX & SEG_MAX feature.
>>>
>>> Add support for those features. Split an io request into multiple virtio
>>> requests if more than seg_max segments would be used. Also split a
>>> single buffer request into multiple segments if the buffer is bigger
>>> then size_max.
>>>
>>> Signed-off-by: Christian Pötzsch <christian.poetzsch@kernkonzept.com>
>>> Signed-off-by: Adam Lackorzynski <adam@l4re.org>
>>
>>> diff --git a/drivers/virtio/virtio_blk.c b/drivers/virtio/virtio_blk.c
>>> @@ -119,7 +145,38 @@ static ulong virtio_blk_do_req(...)
>>> +err_free:
>>> +     for (i = 0; i < seg_cnt + 2; ++i)
>>> +             free(sgs[i]);
>>> +     free(sgs);
>>> +
>>> +     return status == VIRTIO_BLK_S_OK ? blkcnt : -EIO;
>>
>> The err_free label is reached from both the success path (fall-through
>> after virtqueue_get_buf()) and error paths (goto from malloc()
>> failure, virtqueue_add() failure, or unknown type). On error paths,
>> status is uninitialised, so the final check has undefined behaviour.
>> Please can you separate the success path from the error cleanup, e.g.
>> with an explicit return before the err_free label.
Right, the error case is not well defined. However, I can't return before the label, because than the two segments are leaked. At this point the virtio operation has finished, so the segment pointers need to be freed. In v2, I did initialize the status to error instead. Now, the error case is well defined too.

>>
>>> diff --git a/drivers/virtio/virtio_blk.c b/drivers/virtio/virtio_blk.c
>>> @@ -145,38 +145,38 @@ static ulong virtio_blk_do_req(...)
>>> +     while (i < blkcnt) {
>>> +             u32 blk_per_sg = min(blkcnt - i, seg_sec_cnt * priv->seg_max);
>>> +
>>> +             ret = virtio_blk_do_single_req(dev, sector + i, blk_per_sg,
>>> +                                            buffer + i * 512, type);
>>> +             if (!ret)
>>> +                     return ret;
>>
>> The error check is inverted. virtio_blk_do_single_req() returns blkcnt
>> (positive) on success and -EIO on failure, so if (!ret) only triggers
>> when ret is zero. I suspect you want if (ret < 0) here.
Correct, fixed it in v2.

>>
>> BTW please add a function comment for virtio_blk_do_single_req() so
>> all this is clearer.
Done in v2.

> 
> This is all true, and useful feedback.
> 
>>> diff --git a/drivers/virtio/virtio_blk.c b/drivers/virtio/virtio_blk.c
>>> @@ -67,50 +74,69 @@ static void virtio_blk_init_data_sg(...)
>>> +     // The virtio device may have constrains on the maximum segment size.
>>
>> U-Boot follows the Linux kernel coding style which prefers /* */
>> comments over //. Please can you convert these.
> 
> This hasn't been true for a number of years, Linux Kernel nor here.
> We've accepted C99-style comments (when not needing to be kernel-doc)
> for a long time now.
>
Thanks for the info Tom, I still converted the comments in v2.

Thanks
Chris

[PATCH v2] virtio: add support for SIZE_MAX & SEG_MAX features

[Christian Pötzsch]

Some virtio implementations may forward the virtio requests directly to
the underlying hw. The hw may have some restrictions in how many and how
big the requests can be. Therefore, the corresponding virtio device will
announce this limitations with the SIZE_MAX & SEG_MAX feature.

Add support for those features. Split an io request into multiple virtio
requests if more than seg_max segments would be used. Also split a
single buffer request into multiple segments if the buffer is bigger
then size_max.

Signed-off-by: Christian Pötzsch <christian.poetzsch@kernkonzept.com>
Signed-off-by: Adam Lackorzynski <adam@l4re.org>
---
Changes in v2:
- Fixed behavior in error case in virtio_blk_do_req
- Fixed return check in virtio_blk_do_single_req
- Change comment style

 drivers/virtio/virtio_blk.c | 122 +++++++++++++++++++++++++++++-------
 1 file changed, 99 insertions(+), 23 deletions(-)

diff --git a/drivers/virtio/virtio_blk.c b/drivers/virtio/virtio_blk.c
index 3dd0cf36268..45fb596a330 100644
--- a/drivers/virtio/virtio_blk.c
+++ b/drivers/virtio/virtio_blk.c
@@ -14,6 +14,7 @@
 #include <virtio_ring.h>
 #include <linux/log2.h>
 #include "virtio_blk.h"
+#include <malloc.h>
 
 /**
  * struct virtio_blk_priv - private data for virtio block device
@@ -23,10 +24,16 @@ struct virtio_blk_priv {
 	struct virtqueue *vq;
 	/** @blksz_shift - log2 of block size divided by 512 */
 	u32 blksz_shift;
+	/** @size_max - maximum segment size */
+	u32 size_max;
+	/** @seg_max - maximum segment count */
+	u32 seg_max;
 };
 
 static const u32 feature[] = {
 	VIRTIO_BLK_F_BLK_SIZE,
+	VIRTIO_BLK_F_SIZE_MAX,
+	VIRTIO_BLK_F_SEG_MAX,
 	VIRTIO_BLK_F_WRITE_ZEROES
 };
 
@@ -67,50 +74,77 @@ static void virtio_blk_init_data_sg(void *buffer, lbaint_t blkcnt, struct virtio
 	sg->length = blkcnt * 512;
 }
 
-static ulong virtio_blk_do_req(struct udevice *dev, u64 sector,
-			       lbaint_t blkcnt, void *buffer, u32 type)
+/*
+ * Create, execute and wait for one single virtio request. On success the
+ * transferred block count is returned and in the error case -EIO.
+ */
+static ulong virtio_blk_do_single_req(struct udevice *dev, u64 sector,
+				      lbaint_t blkcnt, char *buffer, u32 type)
 {
 	struct virtio_blk_priv *priv = dev_get_priv(dev);
+	/*
+	* The virtio device may have constrains on the maximum segment size.
+	* Calculate how many segments we need.
+	*/
+	u32 seg_cnt = (blkcnt * 512) / priv->size_max + 1;
+	lbaint_t seg_sec_cnt = priv->size_max / 512;
 	struct virtio_blk_outhdr out_hdr;
 	struct virtio_blk_discard_write_zeroes wz_hdr;
 	unsigned int num_out = 0, num_in = 0;
-	struct virtio_sg hdr_sg, wz_sg, data_sg, status_sg;
-	struct virtio_sg *sgs[3];
-	u8 status;
+	struct virtio_sg **sgs;
+	u8 status = VIRTIO_BLK_S_IOERR;
 	int ret;
+	u32 i;
 
-	sector <<= priv->blksz_shift;
-	blkcnt <<= priv->blksz_shift;
-	virtio_blk_init_header_sg(dev, sector, type, &out_hdr, &hdr_sg);
-	sgs[num_out++] = &hdr_sg;
+	/*
+	* +2 is header and status descriptor; seg_cnt is the number of data segments
+	* required. Needs to be dynamically allocated.
+	*/
+	sgs = calloc(seg_cnt + 2, sizeof(struct virtio_sg *));
+	if (!sgs)
+		return -ENOMEM;
+
+	for (i = 0; i < seg_cnt + 2; ++i) {
+		sgs[i] = malloc(sizeof(struct virtio_sg));
+		if (!sgs[i])
+			goto err_free;
+	}
+
+	virtio_blk_init_header_sg(dev, sector, type, &out_hdr, sgs[num_out++]);
 
 	switch (type) {
 	case VIRTIO_BLK_T_IN:
-	case VIRTIO_BLK_T_OUT:
-		virtio_blk_init_data_sg(buffer, blkcnt, &data_sg);
-		if (type & VIRTIO_BLK_T_OUT)
-			sgs[num_out++] = &data_sg;
-		else
-			sgs[num_out + num_in++] = &data_sg;
+	case VIRTIO_BLK_T_OUT: {
+		i = 0;
+		while (i < blkcnt) {
+			u32 blk_per_seg = min(blkcnt - i, seg_sec_cnt);
+
+			if (type & VIRTIO_BLK_T_OUT)
+				virtio_blk_init_data_sg(buffer + i * 512, blk_per_seg,
+							sgs[num_out++]);
+			else
+				virtio_blk_init_data_sg(buffer + i * 512, blk_per_seg,
+							sgs[num_out + num_in++]);
+			i += blk_per_seg;
+		}
 		break;
-
+	}
 	case VIRTIO_BLK_T_WRITE_ZEROES:
-		virtio_blk_init_write_zeroes_sg(dev, sector, blkcnt, &wz_hdr, &wz_sg);
-		sgs[num_out++] = &wz_sg;
+		virtio_blk_init_write_zeroes_sg(dev, sector, blkcnt, &wz_hdr,
+						sgs[num_out++]);
 		break;
 
 	default:
-		return -EINVAL;
+		goto err_free;
 	}
 
-	virtio_blk_init_status_sg(&status, &status_sg);
-	sgs[num_out + num_in++] = &status_sg;
+	virtio_blk_init_status_sg(&status, sgs[num_out + num_in++]);
 	log_debug("dev=%s, active=%d, priv=%p, priv->vq=%p\n", dev->name,
 		  device_active(dev), priv, priv->vq);
 
 	ret = virtqueue_add(priv->vq, sgs, num_out, num_in);
 	if (ret)
-		return ret;
+		goto err_free;
 
 	virtqueue_kick(priv->vq);
 
@@ -119,7 +153,40 @@ static ulong virtio_blk_do_req(struct udevice *dev, u64 sector,
 		;
 	log_debug("done\n");
 
-	return status == VIRTIO_BLK_S_OK ? blkcnt >> priv->blksz_shift : -EIO;
+err_free:
+	for (i = 0; i < seg_cnt + 2; ++i)
+		free(sgs[i]);
+	free(sgs);
+
+	return status == VIRTIO_BLK_S_OK ? blkcnt : -EIO;
+}
+
+static ulong virtio_blk_do_req(struct udevice *dev, u64 sector,
+			       lbaint_t blkcnt, char *buffer, u32 type)
+{
+	struct virtio_blk_priv *priv = dev_get_priv(dev);
+	lbaint_t seg_sec_cnt = priv->size_max / 512;
+	u32 i = 0;
+	ulong ret;
+
+	sector <<= priv->blksz_shift;
+	blkcnt <<= priv->blksz_shift;
+
+	/*
+	* The virtio device may have constrains on the maximum segment count. So
+	* send multiple virtio requests one after each other, if so.
+	*/
+	while (i < blkcnt) {
+		u32 blk_per_sg = min(blkcnt - i, seg_sec_cnt * priv->seg_max);
+
+		ret = virtio_blk_do_single_req(dev, sector + i, blk_per_sg,
+					       buffer + i * 512, type);
+		if (ret < 0)
+			return ret;
+		i += blk_per_sg;
+	}
+
+	return blkcnt >> priv->blksz_shift;
 }
 
 static ulong virtio_blk_read(struct udevice *dev, lbaint_t start,
@@ -207,6 +274,15 @@ static int virtio_blk_probe(struct udevice *dev)
 	priv->blksz_shift = desc->log2blksz - 9;
 	desc->lba >>= priv->blksz_shift;
 
+	if (virtio_has_feature(dev, VIRTIO_BLK_F_SIZE_MAX))
+		virtio_cread(dev, struct virtio_blk_config, size_max, &priv->size_max);
+	else
+		priv->size_max = -1U;
+	if (virtio_has_feature(dev, VIRTIO_BLK_F_SEG_MAX))
+		virtio_cread(dev, struct virtio_blk_config, seg_max, &priv->seg_max);
+	else
+		priv->seg_max = -1U;
+
 	return 0;
 }
 
-- 
2.47.3

Re: [PATCH v2] virtio: add support for SIZE_MAX & SEG_MAX features

[Tom Rini]

On Fri, 17 Apr 2026 14:03:19 +0200, Christian Pötzsch wrote:

> Some virtio implementations may forward the virtio requests directly to
> the underlying hw. The hw may have some restrictions in how many and how
> big the requests can be. Therefore, the corresponding virtio device will
> announce this limitations with the SIZE_MAX & SEG_MAX feature.
> 
> Add support for those features. Split an io request into multiple virtio
> requests if more than seg_max segments would be used. Also split a
> single buffer request into multiple segments if the buffer is bigger
> then size_max.
> 
> [...]

Applied to u-boot/master, thanks!

[1/1] virtio: add support for SIZE_MAX & SEG_MAX features
      commit: bb4142af7ed8c94b3df3e75ca9ab3ef450e80885
-- 
Tom