[RFC PATCH 04/12] s390/cio: introduce cio DMA pool

[Halil Pasic <pasic@linux.ibm.com>]

To support protected virtualization cio will need to make sure the
memory used for communication with the hypervisor is DMA memory.

Let us introduce a DMA pool to cio that will help us in allocating
deallocating those chunks of memory.

We use a gen_pool backed with DMA pages to avoid each allocation
effectively wasting a page, as we typically allocate much less
than PAGE_SIZE.

Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
---
 arch/s390/Kconfig           |  1 +
 arch/s390/include/asm/cio.h |  3 +++
 drivers/s390/cio/css.c      | 57 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 61 insertions(+)

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 46c69283a67b..e8099ab47368 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -194,6 +194,7 @@ config S390
 	select VIRT_TO_BUS
 	select HAVE_NMI
 	select SWIOTLB
+	select GENERIC_ALLOCATOR
 
 
 config SCHED_OMIT_FRAME_POINTER
diff --git a/arch/s390/include/asm/cio.h b/arch/s390/include/asm/cio.h
index 1727180e8ca1..4510e418614a 100644
--- a/arch/s390/include/asm/cio.h
+++ b/arch/s390/include/asm/cio.h
@@ -328,6 +328,9 @@ static inline u8 pathmask_to_pos(u8 mask)
 void channel_subsystem_reinit(void);
 extern void css_schedule_reprobe(void);
 
+extern void *cio_dma_zalloc(size_t size);
+extern void cio_dma_free(void *cpu_addr, size_t size);
+
 /* Function from drivers/s390/cio/chsc.c */
 int chsc_sstpc(void *page, unsigned int op, u16 ctrl, u64 *clock_delta);
 int chsc_sstpi(void *page, void *result, size_t size);
diff --git a/drivers/s390/cio/css.c b/drivers/s390/cio/css.c
index aea502922646..72629d99d8e4 100644
--- a/drivers/s390/cio/css.c
+++ b/drivers/s390/cio/css.c
@@ -20,6 +20,8 @@
 #include <linux/reboot.h>
 #include <linux/suspend.h>
 #include <linux/proc_fs.h>
+#include <linux/genalloc.h>
+#include <linux/dma-mapping.h>
 #include <asm/isc.h>
 #include <asm/crw.h>
 
@@ -886,6 +888,8 @@ static const struct attribute_group *cssdev_attr_groups[] = {
 	NULL,
 };
 
+static u64 css_dev_dma_mask = DMA_BIT_MASK(31);
+
 static int __init setup_css(int nr)
 {
 	struct channel_subsystem *css;
@@ -899,6 +903,9 @@ static int __init setup_css(int nr)
 	dev_set_name(&css->device, "css%x", nr);
 	css->device.groups = cssdev_attr_groups;
 	css->device.release = channel_subsystem_release;
+	/* some cio DMA memory needs to be 31 bit addressable */
+	css->device.coherent_dma_mask = DMA_BIT_MASK(31),
+	css->device.dma_mask = &css_dev_dma_mask;
 
 	mutex_init(&css->mutex);
 	css->cssid = chsc_get_cssid(nr);
@@ -1018,6 +1025,55 @@ static struct notifier_block css_power_notifier = {
 	.notifier_call = css_power_event,
 };
 
+#define POOL_INIT_PAGES 1
+static struct gen_pool *cio_dma_pool;
+/* Currently cio supports only a single css */
+static struct device *cio_dma_css;
+static gfp_t  cio_dma_flags;
+
+static void __init cio_dma_pool_init(void)
+{
+	void *cpu_addr;
+	dma_addr_t dma_addr;
+	int i;
+
+	cio_dma_css = &channel_subsystems[0]->device;
+	cio_dma_flags = GFP_DMA | GFP_KERNEL | __GFP_ZERO;
+	cio_dma_pool = gen_pool_create(3, -1);
+	/* No need to free up the resources: compiled in */
+	for (i = 0; i < POOL_INIT_PAGES; ++i) {
+		cpu_addr = dma_alloc_coherent(cio_dma_css, PAGE_SIZE, &dma_addr,
+					      cio_dma_flags);
+		if (!cpu_addr)
+			return;
+		gen_pool_add_virt(cio_dma_pool, (unsigned long) cpu_addr,
+				  dma_addr, PAGE_SIZE, -1);
+	}
+
+}
+
+void *cio_dma_zalloc(size_t size)
+{
+	dma_addr_t dma_addr;
+	unsigned long addr = gen_pool_alloc(cio_dma_pool, size);
+
+	if (!addr) {
+		addr = (unsigned long) dma_alloc_coherent(cio_dma_css,
+					PAGE_SIZE, &dma_addr, cio_dma_flags);
+		if (!addr)
+			return NULL;
+		gen_pool_add_virt(cio_dma_pool, addr, dma_addr, PAGE_SIZE, -1);
+		addr = gen_pool_alloc(cio_dma_pool, size);
+	}
+	return (void *) addr;
+}
+
+void cio_dma_free(void *cpu_addr, size_t size)
+{
+	memset(cpu_addr, 0, size);
+	gen_pool_free(cio_dma_pool, (unsigned long) cpu_addr, size);
+}
+
 /*
  * Now that the driver core is running, we can setup our channel subsystem.
  * The struct subchannel's are created during probing.
@@ -1063,6 +1119,7 @@ static int __init css_bus_init(void)
 		unregister_reboot_notifier(&css_reboot_notifier);
 		goto out_unregister;
 	}
+	cio_dma_pool_init();
 	css_init_done = 1;
 
 	/* Enable default isc for I/O subchannels. */
-- 
2.16.4