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Message-Id: <20121206000026.A620D3E0E22@localhost> Date: Thu, 06 Dec 2012 00:00:26 +0000 From: Grant Likely <grant.likely@...retlab.ca> To: Mark Brown <broonie@...nsource.wolfsonmicro.com> Cc: spi-devel-general@...ts.sourceforge.net, linux-kernel@...r.kernel.org, Mark Brown <broonie@...nsource.wolfsonmicro.com> Subject: Re: [PATCH] spi: Remove SPI_BUFSIZ restriction on spi_write_then_read() On Sun, 2 Dec 2012 12:54:25 +0900, Mark Brown <broonie@...nsource.wolfsonmicro.com> wrote: > In order to avoid constantly allocating and deallocating there is a fixed > buffer which spi_write_then_read() uses for transfers, with an early error > check to ensure that the transfer fits within the buffer. This limits the > size of transfers to this size, currently max(32, SMP_CACHE_BYTES). > > Since we can dynamically allocate and in fact already have a fallback > to do so when there is contention for the fixed buffer remove this > restriction and instead dynamically allocate a suitably sized buffer if > the transfer won't fit. > > Signed-off-by: Mark Brown <broonie@...nsource.wolfsonmicro.com> Looks good to me. Probably 3.9 material though. Acked-by: Grant Likely <grant.likely@...retlab.ca> > --- > drivers/spi/spi.c | 24 +++++++++++------------- > 1 file changed, 11 insertions(+), 13 deletions(-) > > diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c > index c4f7d71..224b7bc 100644 > --- a/drivers/spi/spi.c > +++ b/drivers/spi/spi.c > @@ -1646,12 +1646,18 @@ int spi_write_then_read(struct spi_device *spi, > struct spi_transfer x[2]; > u8 *local_buf; > > - /* Use preallocated DMA-safe buffer. We can't avoid copying here, > - * (as a pure convenience thing), but we can keep heap costs > - * out of the hot path ... > + /* Use preallocated DMA-safe buffer if we can. We can't avoid > + * copying here, (as a pure convenience thing), but we can > + * keep heap costs out of the hot path unless someone else is > + * using the pre-allocated buffer or the transfer is too large. > */ > - if ((n_tx + n_rx) > SPI_BUFSIZ) > - return -EINVAL; > + if ((n_tx + n_rx) > SPI_BUFSIZ || !mutex_trylock(&lock)) { > + local_buf = kmalloc(max(SPI_BUFSIZ, n_tx + n_rx), GFP_KERNEL); > + if (!local_buf) > + return -ENOMEM; > + } else { > + local_buf = buf; > + } > > spi_message_init(&message); > memset(x, 0, sizeof x); > @@ -1664,14 +1670,6 @@ int spi_write_then_read(struct spi_device *spi, > spi_message_add_tail(&x[1], &message); > } > > - /* ... unless someone else is using the pre-allocated buffer */ > - if (!mutex_trylock(&lock)) { > - local_buf = kmalloc(SPI_BUFSIZ, GFP_KERNEL); > - if (!local_buf) > - return -ENOMEM; > - } else > - local_buf = buf; > - > memcpy(local_buf, txbuf, n_tx); > x[0].tx_buf = local_buf; > x[1].rx_buf = local_buf + n_tx; > -- > 1.7.10.4 > -- Grant Likely, B.Sc, P.Eng. Secret Lab Technologies, Ltd. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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