Re: [PATCH] ata: libata depends on HAS_DMA

[Arnd Bergmann <arnd@arndb.de>]

On Tuesday 12 May 2009, Jeff Garzik wrote:
> > --- a/drivers/ata/Kconfig
> > +++ b/drivers/ata/Kconfig
> > @@ -4,7 +4,7 @@
> >  
> >  menuconfig ATA
> >       tristate "Serial ATA (prod) and Parallel ATA (experimental) drivers"
> > -     depends on HAS_IOMEM
> > +     depends on HAS_IOMEM && HAS_DMA
> >       depends on BLOCK
> >       depends on !(M32R || M68K) || BROKEN
> 
> What specifically is breaking?
> 
> Ideally we should be able to work with PIO-only...

CONFIG_HAS_DMA is not set on architectures that are missing
asm/dma-mapping.h or fall back to asm-generic/dma-mapping-broken.h.

In the latter case, you get a link error:
drivers/built-in.o: In function `sas_issue_ata_cmd':
/home/arnd/linux/linux-2.6/drivers/scsi/libsas/sas_ata.c(.text+0x33c50): undefined reference to `dma_map_sg'
/home/arnd/linux/linux-2.6/drivers/scsi/libsas/sas_ata.c(.text+0x33ef0): undefined reference to `dma_unmap_sg'
drivers/built-in.o: In function `ata_sg_clean':
/home/arnd/linux/linux-2.6/drivers/ata/libata-core.c(.text+0x37d18): undefined reference to `dma_unmap_sg'
drivers/built-in.o: In function `ata_qc_issue':
/home/arnd/linux/linux-2.6/drivers/ata/libata-core.c(.text+0x38774): undefined reference to `dma_map_sg'
drivers/built-in.o: In function `ata_port_start':
/home/arnd/linux/linux-2.6/drivers/ata/libata-core.c(.text+0x3bf0c): undefined reference to `dmam_alloc_coherent'

A slightly less naive (but still suboptimal) fix would be the patch below.
I could not find an easy way to force all devices to use PIO, this
patch would simply fail if someone tried to set a DMA mode.

	Arnd <><

--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -4629,6 +4629,7 @@ static unsigned int ata_dev_init_params(struct ata_device *dev,
  */
 void ata_sg_clean(struct ata_queued_cmd *qc)
 {
+#ifdef CONFIG_HAS_DMA
 	struct ata_port *ap = qc->ap;
 	struct scatterlist *sg = qc->sg;
 	int dir = qc->dma_dir;
@@ -4642,6 +4643,7 @@ void ata_sg_clean(struct ata_queued_cmd *qc)
 
 	qc->flags &= ~ATA_QCFLAG_DMAMAP;
 	qc->sg = NULL;
+#endif /* CONFIG_HAS_DMA */
 }
 
 /**
@@ -4743,6 +4745,7 @@ void ata_sg_init(struct ata_queued_cmd *qc, struct scatterlist *sg,
  */
 static int ata_sg_setup(struct ata_queued_cmd *qc)
 {
+#ifdef CONFIG_HAS_DMA
 	struct ata_port *ap = qc->ap;
 	unsigned int n_elem;
 
@@ -4758,6 +4761,10 @@ static int ata_sg_setup(struct ata_queued_cmd *qc)
 	qc->flags |= ATA_QCFLAG_DMAMAP;
 
 	return 0;
+#else
+	DPRINTK("attempted to use DMA on incompatible architecture\n");
+	return -EINVAL;
+#endif /* CONFIG_HAS_DMA */
 }
 
 /**
@@ -5450,8 +5457,12 @@ int ata_port_start(struct ata_port *ap)
 {
 	struct device *dev = ap->dev;
 
+#ifdef CONFIG_HAS_DMA
 	ap->prd = dmam_alloc_coherent(dev, ATA_PRD_TBL_SZ, &ap->prd_dma,
 				      GFP_KERNEL);
+#else
+	ap->prd = devres_alloc(dev, ATA_PRD_TBL_SZ, GFP_KERNEL);
+#endif /* CONFIG_HAS_DMA */
 	if (!ap->prd)
 		return -ENOMEM;
 
diff --git a/drivers/scsi/libsas/Kconfig b/drivers/scsi/libsas/Kconfig
index 59e00fa..e00271f 100644
--- a/drivers/scsi/libsas/Kconfig
+++ b/drivers/scsi/libsas/Kconfig
@@ -34,6 +34,7 @@ config SCSI_SAS_ATA
 	bool "ATA support for libsas (requires libata)"
 	depends on SCSI_SAS_LIBSAS
 	depends on ATA = y || ATA = SCSI_SAS_LIBSAS
+	depends on HAS_DMA
 	help
 		Builds in ATA support into libsas.  Will necessitate
 		the loading of libata along with libsas.