strange segfaults with CompactFlash in "true-ide" mode on PXA270

[schindele@nentec.de (Juergen Schindele)]

Am Mittwoch, 23. Juni 2010 schrieb Lothar Wa?mann:
> Hi,
> 
> > we have a strange problem when booting from a Compact Flash card
> > as root-device. In one of 10 cases while booting an application from
> > root-filesystem dies with "Segmentation fault" without a visible error.
> > After booting the same application runs hundred times without error.
> > (we're talking about standard appl. like chat, pppd, hwclock and so on)
> > 
> > For debugging purposes we put printk's in kernels IDE driver 
> > and the problem disappeared. But replacing the printk by a usleep
> > or so (which is not a solution !) brings the problem back.
> > It seems that the application received faulty data from CF.
> > But how and why ?????????????????????????????
> > 
> > We tested with a custom PXA270 board with a CompactFlash in 
> > "true ide" on processor bus driven by "generic ide / pata_platform"
> > driver from linux-2.6.27.x.
> > (by the way linux-2.6.20.x showed the same problem).
> > 
> > Any ideas, hints, experiences, patches are very welcome :-)
> > --------------------------------------------------------------
> I guess that is the old cache problem that apparently was never really
> fixed:
> http://marc.info/?t=108537828400002&r=1&w=2
Hello
this hint was very helpful for understanding the problem.
In the mail from Russell King at 
<http://marc.info/?l=linux-arm-kernel&m=108611676807909&w=2>
he said : .... the rule is if the CPU writes to a page cache page,
it must call flush_dcache_page afterwards to ensure cache coherency with user space".

so i made the following patch in drivers/ide/ide-taskfile.c
in the function ide_pio_sector() where blocks from disk are read
into a cached page to apply the rule from Russell. 
===================================================================
--- ide-taskfile.c
+++ ide-taskfile.c.new
@@ -278,6 +278,7 @@
                hwif->tp_ops->input_data(drive, rq, buf, SECTOR_SIZE);

        kunmap_atomic(buf, KM_BIO_SRC_IRQ);
+       flush_dcache_page(page);
 #ifdef CONFIG_HIGHMEM
        local_irq_restore(flags);
 #endif

And from there on the problem disappeared :-))
What are you think about ???
Isn't this missing for years in IDE PIO driver ???
--------------------------------------------------------------
J?rgen Schindele  
Software-Entwicklung

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