>-----Original Message-----
>From: Mike Frysinger [mailto:[email protected]]
>Sent: Thursday, December 10, 2009 11:08 AM
>To: Song, Barry
>Cc: [email protected];
>[email protected]
>Subject: Re: [Linux-kernel-commits] [7906]
>trunk/arch/blackfin: task [#5723], Enable 128/256k/ 512k
>uncacheable DMA memory region for small memory system
>
>On Wed, Dec 9, 2009 at 21:18, Song, Barry wrote:
>>From: Mike Frysinger [mailto:[email protected]]
>>>On Wed, Dec 2, 2009 at 04:13, <[email protected]> wrote:
>>>> Revision 7906 Author bhsong Date 2009-12-02 04:13:36 -0500
>>>>
>>>> Log Message
>>>>
>>>> task [#5723], Enable 128/256k/512k uncacheable DMA memory
>>>> region for small memory system
>>>>
>>>> Modified: trunk/arch/blackfin/kernel/cplb-nompu/cplbinit.c
>(7905 => 7906)
>>>>
>>>> @@ -136,10 +146,22 @@
>>>> i_i = 0;
>>>> /* Normal RAM, including MTD FS. */
>>>> #ifdef CONFIG_MTD_UCLINUX
>>>> - icplb_bounds[i_i].eaddr = memory_mtd_start + mtd_size;
>>>> + /*
>>>> + * While DMA uncache size is 128/256/512KB, we let
>>>>icplb cover the whole
>>>> 1MB from normal_memory_end & 0xfffff
>>>> + * A bad result is the 128/256/512KB becomes be able to fetch
>>>> instrcutions. But in order to protect the area,
>>>> + * we have to manage the area by page size
>>>> + */
>>>> + if (unlikely((memory_mtd_start + mtd_size) & (1 * 1024
>>>>* 1024 - 1)))
>>>> + icplb_bounds[i_i].eaddr = ((memory_mtd_start +
>>>>mtd_size) & ~(1 * 1024 *
>>>> 1024 - 1)) + 1 * 1024 * 1024;
>>>> + else
>>>> + icplb_bounds[i_i].eaddr = memory_mtd_start + mtd_size;
>>>> #else
>>>> - icplb_bounds[i_i].eaddr = memory_end;
>>>> + if (unlikely(memory_end & (1 * 1024 * 1024 - 1)))
>>>> + icplb_bounds[i_i].eaddr = (memory_end & ~(1 *
>>>>1024 * 1024 - 1)) + 1 *
>>>> 1024 * 1024;
>>>> + else
>>>> + icplb_bounds[i_i].eaddr = memory_end;
>>>> #endif
>>>> +
>>>> icplb_bounds[i_i++].data = SDRAM_IGENERIC;
>>>> /* DMA uncached region. */
>>>> if (DMA_UNCACHED_REGION) {
>>>
>>>while i can understand the need to change the DCPLB maps, why do we
>>>need this for ICPLBs ? the dma uncached region is reserved for data
>>>usage ... we're never going to put instructions in there.
>>
>> Not exact. If DMA uncache size is less than 1MB, normal
>memory end will
>> not be 1MB aligned. Then the last "1MB - DMA uncached size" will be
>> difficult to be covered by any icplb.
>> Here we just give more space to normal memory. As I comment, a bad
>> result is the 128/256/512KB DMA area becomes be able to fetch
>> instrcutions.
>
>i know normal memory wont be exactly aligned. i'm saying that for the
>purposes of icplb's, why do we care. there shouldnt be an icplb miss
>in the uncached region, so simply giving icplb coverage to the whole
>thing shouldnt matter. same goes for the if (DMA_UNCACHED_REGION)
>icplb code. we should simply cover all memory that the kernel is
>managing (i.e. everything up to _ramend).
I can agree that.
>-mike
>
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