[PATCH v2 2/2] drm/omap: partial workaround for DRA7xx DMM errata i878
Laurent Pinchart
laurent.pinchart at ideasonboard.com
Tue Apr 3 21:11:31 UTC 2018
Hi Peter,
Thank you for the patch.
On Thursday, 22 March 2018 15:42:06 EEST Peter Ujfalusi wrote:
> From: Tomi Valkeinen <tomi.valkeinen at ti.com>
>
> Errata i878 says that MPU should not be used to access RAM and DMM at
> the same time. As it's not possible to prevent MPU accessing RAM, we
> need to access DMM via a proxy.
>
> This patch changes DMM driver to access DMM registers via sDMA. Instead
> of doing a normal readl/writel call to read/write a register, we use
> sDMA to copy 4 bytes from/to the DMM registers.
>
> This patch provides only a partial workaround for i878, as not only DMM
> register reads/writes are affected, but also accesses to the DMM mapped
> buffers (framebuffers, usually).
I assume access to DMM-mapped buffers to be way more frequent than access to
the DMM registers. If that's the case, this partial workaround should only
slightly lower the probability of system lock-up. Do you have plans to
implement a workaround that will fix the problem completely ?
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen at ti.com>
> ---
> drivers/gpu/drm/omapdrm/omap_dmm_priv.h | 8 ++
> drivers/gpu/drm/omapdrm/omap_dmm_tiler.c | 153 +++++++++++++++++++++++++++-
> 2 files changed, 159 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/omapdrm/omap_dmm_priv.h
> b/drivers/gpu/drm/omapdrm/omap_dmm_priv.h index c2785cc98dc9..9ce9d1d7039a
> 100644
> --- a/drivers/gpu/drm/omapdrm/omap_dmm_priv.h
> +++ b/drivers/gpu/drm/omapdrm/omap_dmm_priv.h
> @@ -155,10 +155,12 @@ struct refill_engine {
>
> struct dmm_platform_data {
> u32 cpu_cache_flags;
> + bool errata_i878_wa;
> };
>
> struct dmm {
> struct device *dev;
> + dma_addr_t phys_base;
> void __iomem *base;
> int irq;
>
> @@ -189,6 +191,12 @@ struct dmm {
> struct list_head alloc_head;
>
> const struct dmm_platform_data *plat_data;
> +
> + bool dmm_workaround;
> + spinlock_t wa_lock;
> + u32 *wa_dma_data;
> + dma_addr_t wa_dma_handle;
> + struct dma_chan *wa_dma_chan;
> };
>
> #endif
> diff --git a/drivers/gpu/drm/omapdrm/omap_dmm_tiler.c
> b/drivers/gpu/drm/omapdrm/omap_dmm_tiler.c index e84871e74615..27c67bc36203
> 100644
> --- a/drivers/gpu/drm/omapdrm/omap_dmm_tiler.c
> +++ b/drivers/gpu/drm/omapdrm/omap_dmm_tiler.c
> @@ -18,6 +18,7 @@
> #include <linux/completion.h>
> #include <linux/delay.h>
> #include <linux/dma-mapping.h>
> +#include <linux/dmaengine.h>
> #include <linux/errno.h>
> #include <linux/init.h>
> #include <linux/interrupt.h>
> @@ -79,14 +80,138 @@ static const u32 reg[][4] = {
> DMM_PAT_DESCR__2, DMM_PAT_DESCR__3},
> };
>
> +static int dmm_dma_copy(struct dmm *dmm, dma_addr_t src, dma_addr_t dst)
> +{
> + struct dma_device *dma_dev = dmm->wa_dma_chan->device;
> + struct dma_async_tx_descriptor *tx;
> + enum dma_status status;
> + dma_cookie_t cookie;
> +
> + tx = dma_dev->device_prep_dma_memcpy(dmm->wa_dma_chan, dst, src, 4, 0);
> + if (!tx) {
> + dev_err(dmm->dev, "Failed to prepare DMA memcpy\n");
> + return -EIO;
> + }
> +
> + cookie = tx->tx_submit(tx);
> + if (dma_submit_error(cookie)) {
> + dev_err(dmm->dev, "Failed to do DMA tx_submit\n");
> + return -EIO;
> + }
> +
> + dma_async_issue_pending(dmm->wa_dma_chan);
> + status = dma_sync_wait(dmm->wa_dma_chan, cookie);
dma_sync_wait() has a 5s timeout. You're calling this function with a spinlock
held. The end result might be slightly better than a complete system lock as
caused by the bug described in i878, but only slightly.
Unless I'm mistaken the reason you can't sleep here is because of the need to
access registers in the interrupt handler. Could we use threaded IRQs to solve
this ?
> + if (status != DMA_COMPLETE)
> + dev_err(dmm->dev, "i878 wa DMA copy failure\n");
> +
> + dmaengine_terminate_all(dmm->wa_dma_chan);
> + return 0;
> +}
> +
> +static u32 dmm_read_wa(struct dmm *dmm, u32 reg)
> +{
> + dma_addr_t src, dst;
> + int r;
> +
> + src = dmm->phys_base + reg;
> + dst = dmm->wa_dma_handle;
> +
> + r = dmm_dma_copy(dmm, src, dst);
> + if (r) {
> + dev_err(dmm->dev, "sDMA read transfer timeout\n");
> + return readl(dmm->base + reg);
> + }
> +
> + /*
> + * As per i878 workaround, the DMA is used to access the DMM registers.
> + * Make sure that the readl is not moved by the compiler or the CPU
> + * earlier than the DMA finished writing the value to memory.
> + */
> + rmb();
> + return readl(dmm->wa_dma_data);
> +}
> +
> +static void dmm_write_wa(struct dmm *dmm, u32 val, u32 reg)
> +{
> + dma_addr_t src, dst;
> + int r;
> +
> + writel(val, dmm->wa_dma_data);
> + /*
> + * As per i878 workaround, the DMA is used to access the DMM registers.
> + * Make sure that the writel is not moved by the compiler or the CPU, so
> + * the data will be in place before we start the DMA to do the actual
> + * register write.
> + */
> + wmb();
> +
> + src = dmm->wa_dma_handle;
> + dst = dmm->phys_base + reg;
> +
> + r = dmm_dma_copy(dmm, src, dst);
> + if (r) {
> + dev_err(dmm->dev, "sDMA write transfer timeout\n");
> + writel(val, dmm->base + reg);
> + }
> +}
> +
> static u32 dmm_read(struct dmm *dmm, u32 reg)
> {
> - return readl(dmm->base + reg);
> + if (dmm->dmm_workaround) {
> + u32 v;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&dmm->wa_lock, flags);
> + v = dmm_read_wa(dmm, reg);
> + spin_unlock_irqrestore(&dmm->wa_lock, flags);
> +
> + return v;
> + } else {
> + return readl(dmm->base + reg);
> + }
> }
>
> static void dmm_write(struct dmm *dmm, u32 val, u32 reg)
> {
> - writel(val, dmm->base + reg);
> + if (dmm->dmm_workaround) {
> + unsigned long flags;
> +
> + spin_lock_irqsave(&dmm->wa_lock, flags);
> + dmm_write_wa(dmm, val, reg);
> + spin_unlock_irqrestore(&dmm->wa_lock, flags);
> + } else {
> + writel(val, dmm->base + reg);
> + }
> +}
> +
> +static int dmm_workaround_init(struct dmm *dmm)
> +{
> + dma_cap_mask_t mask;
> +
> + spin_lock_init(&dmm->wa_lock);
> +
> + dmm->wa_dma_data = dma_alloc_coherent(dmm->dev, sizeof(u32),
> + &dmm->wa_dma_handle, GFP_KERNEL);
> + if (!dmm->wa_dma_data)
> + return -ENOMEM;
> +
> + dma_cap_zero(mask);
> + dma_cap_set(DMA_MEMCPY, mask);
> +
> + dmm->wa_dma_chan = dma_request_channel(mask, NULL, NULL);
> + if (!dmm->wa_dma_chan) {
> + dma_free_coherent(dmm->dev, 4, dmm->wa_dma_data, dmm->wa_dma_handle);
> + return -ENODEV;
> + }
> +
> + return 0;
> +}
> +
> +static void dmm_workaround_uninit(struct dmm *dmm)
> +{
> + dma_release_channel(dmm->wa_dma_chan);
> +
> + dma_free_coherent(dmm->dev, 4, dmm->wa_dma_data, dmm->wa_dma_handle);
> }
>
> /* simple allocator to grab next 16 byte aligned memory from txn */
> @@ -632,6 +757,9 @@ static int omap_dmm_remove(struct platform_device *dev)
> if (omap_dmm->dummy_page)
> __free_page(omap_dmm->dummy_page);
>
> + if (omap_dmm->dmm_workaround)
> + dmm_workaround_uninit(omap_dmm);
> +
> if (omap_dmm->irq > 0)
> free_irq(omap_dmm->irq, omap_dmm);
>
> @@ -680,6 +808,7 @@ static int omap_dmm_probe(struct platform_device *dev)
> goto fail;
> }
>
> + omap_dmm->phys_base = mem->start;
> omap_dmm->base = ioremap(mem->start, SZ_2K);
>
> if (!omap_dmm->base) {
> @@ -695,6 +824,17 @@ static int omap_dmm_probe(struct platform_device *dev)
>
> omap_dmm->dev = &dev->dev;
>
> + if (omap_dmm->plat_data->errata_i878_wa) {
> + if (!dmm_workaround_init(omap_dmm)) {
> + omap_dmm->dmm_workaround = true;
> + dev_info(&dev->dev,
> + "workaround for errata i878 in use\n");
> + } else {
> + dev_warn(&dev->dev,
> + "failed to initialize work-around for i878\n");
> + }
> + }
> +
> hwinfo = dmm_read(omap_dmm, DMM_PAT_HWINFO);
> omap_dmm->num_engines = (hwinfo >> 24) & 0x1F;
> omap_dmm->num_lut = (hwinfo >> 16) & 0x1F;
> @@ -1058,6 +1198,11 @@ static const struct dmm_platform_data
> dmm_omap5_platform_data = { .cpu_cache_flags = OMAP_BO_UNCACHED,
> };
>
> +static const struct dmm_platform_data dmm_dra7_platform_data = {
> + .cpu_cache_flags = OMAP_BO_UNCACHED,
> + .errata_i878_wa = true,
> +};
> +
> static const struct of_device_id dmm_of_match[] = {
> {
> .compatible = "ti,omap4-dmm",
> @@ -1067,6 +1212,10 @@ static const struct of_device_id dmm_of_match[] = {
> .compatible = "ti,omap5-dmm",
> .data = &dmm_omap5_platform_data,
> },
> + {
> + .compatible = "ti,dra7-dmm",
> + .data = &dmm_dra7_platform_data,
> + },
> {},
> };
> #endif
--
Regards,
Laurent Pinchart
More information about the dri-devel
mailing list