3fbd432231
While performing R/W access in PIO mode, the common SDHCI driver checks the buffer ready status once per whole block processing. That is, after getting an appropriate interrupt, or checking an appropriate status bit, the driver makes buffer accesses for the whole block size (e.g. 128 reads for 512 bytes block). This is done in accordance with SD Host Controller Specification. At the same time, the Ultra Secured Digital Host Controller (uSDHC), used in i.MX6 (and, probably, earlier i.MX series too), uses a separate Watermark Levels register, controlling the amount of data or space available when raising status bit or interrupt. For default watermark setting of 16 words, the controller expects (and guarantees) no more than 16 buffer accesses after raising buffer ready status bit and generating an appropriate interrupt. If the driver tries to access the whole block size, it will get incorrect data at the end, and a new interrupt will appear later, when the driver already doesn't expect it. This happens sometimes, more likely on low frequencies, e.g. when reading EXT_CSD at MMC card initialization phase (which makes that initialization fail). Such behavior of i.MX uSDHC seems to be non-compliant to SDHCI Specification, but this is the way it works now. In order not to rewrite the SDHCI driver PIO mode access logic, the IMX specific driver can just set the watermark level to default block size (128 words or 512 bytes), so that the controller behavior will be consistent to generic specification. This patch does this for PIO mode accesses only, restoring default values for DMA accesses to avoid any possible side effects from performance point of view. Signed-off-by: Andrew Gabbasov <andrew_gabbasov@mentor.com> Signed-off-by: Harish Jenny K N <harish_kandiga@mentor.com> Acked-by: Adrian Hunter <adrian.hunter@intel.com> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.