Re: [PATCH 03/14] mmc: sdhci: Replace kmap_atomic() with kmap_local_page()

[Adrian Hunter <adrian.hunter@intel.com>]

On 6/10/22 10:03, Avri Altman wrote:
>> kmap_local_page() is equivalent to kmap_atomic() except that it does not
>> disable page faults or preemption. Where possible kmap_local_page() is
>> preferred to kmap_atomic() - refer kernel highmem documentation.
>>
>> In this case, there is no need to disable page faults or preemption, so replace
>> kmap_atomic() with kmap_local_page(), and, correspondingly,
>> kunmap_atomic() with kunmap_local().
>>
>> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
>> ---
>>  drivers/mmc/host/sdhci.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c index
>> 31d87ec7d055..fb6e9a81f198 100644
>> --- a/drivers/mmc/host/sdhci.c
>> +++ b/drivers/mmc/host/sdhci.c
>> @@ -697,12 +697,12 @@ static int sdhci_pre_dma_transfer(struct sdhci_host
>> *host,
>>
>>  static char *sdhci_kmap_atomic(struct scatterlist *sg)  {
>> -       return kmap_atomic(sg_page(sg)) + sg->offset;
>> +       return kmap_local_page(sg_page(sg)) + sg->offset;
>>  }
>>
>>  static void sdhci_kunmap_atomic(void *buffer)  {
>> -       kunmap_atomic(buffer);
>> +       kunmap_local(buffer);
> kmap_local_page documentation, indicates that the unmapping should be done in reverse order.
> Isn't it something that the callers of sdhci_kunmap_atomic now needs to attend?

Nesting is strictly ordered in either case, so there is no change there.
i.e. the map management is stack based