Messages in this thread | | | Date | Wed, 30 Apr 2014 07:54:18 +0200 | From | Darek Marcinkiewicz <> | Subject | Re: [PATCH v2 1/1] Driver for Beckhoff CX5020 EtherCAT master module. |
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On Tue, Apr 29, 2014 at 03:45:08PM -0400, David Miller wrote: > From: Darek Marcinkiewicz <reksio@newterm.pl> > Date: Mon, 28 Apr 2014 07:36:58 +0200 > > > +void *ec_bh_alloc_dma_mem(struct bh_priv *priv, > > + int channel, > > + u8 **buf, > > + dma_addr_t *phys, > > + dma_addr_t *phys_buf, > > + size_t *len) { > > + u32 mask; > > + int offset = channel * DMA_CHAN_SIZE + DMA_CHAN_OFFSET; > > + > > + iowrite32(0xffffffff, priv->dma_io + offset); > > + > > + mask = ioread32(priv->dma_io + offset); > > + mask &= 0xfffffffc; > > + dev_info(PRIV_TO_DEV(priv), > > + "Read mask %x for channel %d\n", > > + mask, channel); > > + *len = ~mask + 1; > > + > > + dev_info(PRIV_TO_DEV(priv), > > + "Allocating %d bytes for channel %d", > > + (int)*len, channel); > > + *buf = pci_alloc_consistent(priv->dev, > > + *len * 2, > > + phys_buf); > > This is really confusing, the log message says that it allocates > "*len" bytes, but actually you are allocating "*len * 2" bytes as > per the arguments you are passing into pci_alloc_consistent. > > Either one or the other is wrong, and if "*len * 2" is the correct > size then it should be explained why you're doubling this value > but providing just plain "*len" to the caller. > > All of these *len values seem to be doubled over and over again, > in the memset() calls, in the pci_free_consistent() calls during > resource release on probe error and driver shutdown. > > Why not just assign X * 2 to *len and get rid of this doubling all > over the place? > This device imposes some limitations on location and size of the buffers that it dma data from/to. It has a "mask" parameter saying two things: 1. RX/TX buffers have to be aligned to "mask" bits. 2. Their max size is 2^mask. In order to have a buffer meeting above criteria driver allocates chunk of size 2 * max buffer size, and half of this chunk gets used later on. So, len here is the size of that aligned buffer, whereas 2 * len is how much memory was actually allocated.
So, yes, this is a little bit confusing. I'll try to clean this up a little bit and send updated patch.
Thank you!
-- DM
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