linux-kernel - Re: [PATCH v12 2/9] dma-buf: dma-heap: export declared functions

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Message-ID: <9ca0e8b7b644637101f8bbc3f69cb71f20665f04.camel@ndufresne.ca>
Date: Thu, 02 Oct 2025 08:40:35 -0400
From: Nicolas Dufresne <nicolas@...fresne.ca>
To: Maxime Ripard <mripard@...hat.com>, Jens Wiklander
	 <jens.wiklander@...aro.org>
Cc: linux-kernel@...r.kernel.org, linux-media@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org, 
	op-tee@...ts.trustedfirmware.org, linux-arm-kernel@...ts.infradead.org, 
 Olivier Masse <olivier.masse@....com>, Thierry Reding
 <thierry.reding@...il.com>, Yong Wu <yong.wu@...iatek.com>,  Sumit Semwal
 <sumit.semwal@...aro.org>, Benjamin Gaignard
 <benjamin.gaignard@...labora.com>, Brian Starkey	 <Brian.Starkey@....com>,
 John Stultz <jstultz@...gle.com>, "T . J . Mercier"	
 <tjmercier@...gle.com>, Christian König	
 <christian.koenig@....com>, Sumit Garg <sumit.garg@...nel.org>, Matthias
 Brugger <matthias.bgg@...il.com>, AngeloGioacchino Del Regno	
 <angelogioacchino.delregno@...labora.com>, azarrabi@....qualcomm.com,
 Simona Vetter <simona.vetter@...ll.ch>, Daniel Stone
 <daniel@...ishbar.org>, Rouven Czerwinski	 <rouven.czerwinski@...aro.org>,
 robin.murphy@....com, Sumit Garg	 <sumit.garg@....qualcomm.com>
Subject: Re: [PATCH v12 2/9] dma-buf: dma-heap: export declared functions

Le jeudi 02 octobre 2025 à 09:47 +0200, Maxime Ripard a écrit :
> Hi,
> 
> On Thu, Sep 11, 2025 at 03:49:43PM +0200, Jens Wiklander wrote:
> > Export the dma-buf heap functions to allow them to be used by the OP-TEE
> > driver. The OP-TEE driver wants to register and manage specific secure
> > DMA heaps with it.
> > 
> > Reviewed-by: Sumit Garg <sumit.garg@....qualcomm.com>
> > Reviewed-by: T.J. Mercier <tjmercier@...gle.com>
> > Acked-by: Sumit Semwal <sumit.semwal@...aro.org>
> > Signed-off-by: Jens Wiklander <jens.wiklander@...aro.org>
> > ---
> >  drivers/dma-buf/dma-heap.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c
> > index 3cbe87d4a464..8ab49924f8b7 100644
> > --- a/drivers/dma-buf/dma-heap.c
> > +++ b/drivers/dma-buf/dma-heap.c
> > @@ -11,6 +11,7 @@
> >  #include <linux/dma-buf.h>
> >  #include <linux/dma-heap.h>
> >  #include <linux/err.h>
> > +#include <linux/export.h>
> >  #include <linux/list.h>
> >  #include <linux/nospec.h>
> >  #include <linux/syscalls.h>
> > @@ -202,6 +203,7 @@ void *dma_heap_get_drvdata(struct dma_heap *heap)
> >  {
> >  	return heap->priv;
> >  }
> > +EXPORT_SYMBOL_NS_GPL(dma_heap_get_drvdata, "DMA_BUF_HEAP");
> >  
> >  /**
> >   * dma_heap_get_name - get heap name
> > @@ -214,6 +216,7 @@ const char *dma_heap_get_name(struct dma_heap *heap)
> >  {
> >  	return heap->name;
> >  }
> > +EXPORT_SYMBOL_NS_GPL(dma_heap_get_name, "DMA_BUF_HEAP");
> >  
> >  /**
> >   * dma_heap_add - adds a heap to dmabuf heaps
> > @@ -303,6 +306,7 @@ struct dma_heap *dma_heap_add(const struct
> > dma_heap_export_info *exp_info)
> >  	kfree(heap);
> >  	return err_ret;
> >  }
> > +EXPORT_SYMBOL_NS_GPL(dma_heap_add, "DMA_BUF_HEAP");
> 
> It's not clear to me why we would need to export those symbols.
> 
> As far as I know, heaps cannot be removed, and compiling them as module
> means that we would be able to remove them.
> 
> Now, if we don't expect the users to be compiled as modules, then we
> don't need to export these symbols at all.

Maybe I'm getting out of topic, sorry if its the case, but making that a hard
rule seems very limiting. Didn't we said that a heap driver could be made to
represent memory region on a remote device such as an eGPU ?

Nicolas

> 
> Am I missing something?
> 
> Maxime

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