Re: [PATCH] spi: Fix incomplete handling of SPI_MASTER_MUST_RX/_MUST_TX

From	Mark Brown <broonie@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH] spi: Fix incomplete handling of SPI_MASTER_MUST_RX/_MUST_TX
Date	2016-02-08 17:20 +0100
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On Fri, Feb 05, 2016 at 10:30:24AM +0530, Purna Chandra Mandal wrote:

Please fix your mail client to word wrap within paragraphs at something
substantially less than 80 columns.  Doing this makes your messages much
easier to read and reply to.

> Idea is good, but not sufficient.
> Dummy buffers are _reallocated_ to accommodate larger size of transfer. In this if
> [originally NULL] .rx_buf/.tx_buf is not reset back to NULL after the transfer
> is over spi-core will find those .rx/tx_buf non-NULL in next _transfer() call and
> will pass the stale rx/tx_buf to spi controller driver which will definitely
> corrupt the memory and crash the system.

This needs to be clear to readers; a fairly obvious way of dealing with
this would be to rellocate down to a page rather than freeing.

> Above all the whole design depends on trust that core will not play with any data-structure
> which will break object-oriented/layered approach. So better to undo the modification
> (when needed to facilitate some functionality) unless core wants those information to be passed
> back to caller/client for reporting success or error or else.

That's really not the case, we already make a range of other
modifications to complete partially filled transfers in order to
simplify driver code.

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[PATCH] spi: Fix incomplete handling of SPI_MASTER_MUST_RX/_MUST_TX Joshua Henderson <joshua.henderson@microchip.com> - 2016-02-01 23:40 +0100
  Re: [PATCH] spi: Fix incomplete handling of  SPI_MASTER_MUST_RX/_MUST_TX Mark Brown <broonie@kernel.org> - 2016-02-02 00:20 +0100
    Re: [PATCH] spi: Fix incomplete handling of  SPI_MASTER_MUST_RX/_MUST_TX Purna Chandra Mandal <purna.mandal@microchip.com> - 2016-02-05 06:10 +0100
      Re: [PATCH] spi: Fix incomplete handling of  SPI_MASTER_MUST_RX/_MUST_TX Mark Brown <broonie@kernel.org> - 2016-02-08 17:20 +0100

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