Messages in this thread Patch in this message | | | Date | Fri, 2 Feb 2018 04:47:54 +0200 | From | "Michael S. Tsirkin" <> | Subject | Re: [PATCH v11 2/4] fw_cfg: do DMA read operation |
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On Thu, Feb 01, 2018 at 02:02:58PM +0100, Marc-André Lureau wrote: > Modify fw_cfg_read_blob() to use DMA if the device supports it. > Return errors, because the operation may fail. > > The DMA operation is expected to run synchronously with today qemu, > but the specification states that it may become async, so we run > "control" field check in a loop for eventual changes. > > We may want to switch all the *buf addresses to use only kmalloc'ed > buffers (instead of using stack/image addresses with dma=false). > > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
This seems to cause no end of pain. I see no reason to keep pushing this patch until it's all much more stable.
Something like the below would disable it temporarily.
commit 05054fca8b96900f6b54ab0056458f92b616d74c Author: Michael S. Tsirkin <mst@redhat.com> Date: Fri Feb 2 04:29:59 2018 +0200
fixup! fw_cfg: do DMA read operation
diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c index d86ad92..33e0256 100644 --- a/drivers/firmware/qemu_fw_cfg.c +++ b/drivers/firmware/qemu_fw_cfg.c @@ -41,6 +41,9 @@ MODULE_AUTHOR("Gabriel L. Somlo <somlo@cmu.edu>"); MODULE_DESCRIPTION("QEMU fw_cfg sysfs support"); MODULE_LICENSE("GPL"); +/* enable DMA for all accesses */ +#define FW_CFG_DMA_READ_ENABLE 0 + /* selector key values for "well-known" fw_cfg entries */ #define FW_CFG_SIGNATURE 0x00 #define FW_CFG_ID 0x01 @@ -171,7 +174,7 @@ static ssize_t fw_cfg_read_blob(struct device *dev, u16 key, } mutex_lock(&fw_cfg_dev_lock); - if (dma && fw_cfg_dma_enabled()) { + if (FW_CFG_DMA_READ_ENABLE && dma && fw_cfg_dma_enabled()) { if (pos == 0) { ret = fw_cfg_dma_transfer(dev, buf, count, key << 16 | FW_CFG_DMA_CTL_SELECT
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