On Fri, May 17, 2024 at 01:02:56AM +0530, Mukesh Ojha wrote:
> If we disable CONFIG_ZONE_DMA32 to make the selection of DMA
> memory from higher 4GB range. dma_alloc_coherant() api usage
dma_alloc_coherent()
> inside qcom_scm_pas_init_image() which usage scm 32bit device
> will fail for size of data passed less than PAGE_SIZE and
> it will fallback to buddy pool to allocate memory from which
> will fail.
I interpreted this as:
When CONFIG_ZONE_DMA32 is disabled, dma_alloc_coherent() fails when size
is < PAGE_SIZE. qcom_scm_pas_init_image() will fail to allocate using
dma_alloc_coherent() and incorrectly fall back to buddy pool.
This justification seems incorrect to me. None of the other
dma_alloc_coherent() users are page-aligning their requests in scm
driver. Is something else going on?
>
> Convert the size to aligned to PAGE_SIZE before it gets pass
> to dma_alloc_coherant(), so that it gets coherant memory in
dma_alloc_coherent coherent
> lower 4GB from linux cma region.
>
> Signed-off-by: Mukesh Ojha <quic_mojha@xxxxxxxxxxx>
> ---
> drivers/firmware/qcom/qcom_scm.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
> index 029ee5edbea6..6616048f1c33 100644
> --- a/drivers/firmware/qcom/qcom_scm.c
> +++ b/drivers/firmware/qcom/qcom_scm.c
> @@ -562,6 +562,7 @@ static void qcom_scm_set_download_mode(u32 dload_mode)
> int qcom_scm_pas_init_image(u32 peripheral, const void *metadata, size_t size,
> struct qcom_scm_pas_metadata *ctx)
> {
> + size_t page_aligned_size;
> dma_addr_t mdata_phys;
> void *mdata_buf;
> int ret;
> @@ -579,7 +580,8 @@ int qcom_scm_pas_init_image(u32 peripheral, const void *metadata, size_t size,
> * data blob, so make sure it's physically contiguous, 4K aligned and
> * non-cachable to avoid XPU violations.
> */
> - mdata_buf = dma_alloc_coherent(__scm->dev, size, &mdata_phys,
> + page_aligned_size = PAGE_ALIGN(size + PAGE_SIZE);
Isn't PAGE_ALIGN(size) good enough? Why do you need to round up to the
2nd page? Maybe you thought PAGE_ALIGN was PAGE_ALIGN_DOWN ?
> + mdata_buf = dma_alloc_coherent(__scm->dev, page_aligned_size, &mdata_phys,
> GFP_KERNEL);
> if (!mdata_buf)
> return -ENOMEM;
> @@ -604,11 +606,11 @@ int qcom_scm_pas_init_image(u32 peripheral, const void *metadata, size_t size,
>
> out:
> if (ret < 0 || !ctx) {
> - dma_free_coherent(__scm->dev, size, mdata_buf, mdata_phys);
> + dma_free_coherent(__scm->dev, page_aligned_size, mdata_buf, mdata_phys);
> } else if (ctx) {
> ctx->ptr = mdata_buf;
> ctx->phys = mdata_phys;
> - ctx->size = size;
> + ctx->size = page_aligned_size;
> }
>
> return ret ? : res.result[0];
> --
> 2.7.4
>
>
