cxl: Add cxl_slot_is_supported API
This extends the check that the adapter is in a CAPI capable slot so that it may be called by external users in the kernel API. This will be used by the upcoming Mellanox CX4 support, which needs to know ahead of time if the card can be switched to cxl mode so that it can leave it in PCI mode if it is not. This API takes a parameter to check if CAPP DMA mode is supported, which it currently only allows on P8NVL systems, since that mode currently has issues accessing memory < 4GB on P8, and we cannot realistically avoid that. This API does not currently check if a CAPP unit is available (i.e. not already assigned to another PHB) on P8. Doing so would be racy since it is assigned on a first come first serve basis, and so long as CAPP DMA mode is not supported on P8 we don't need this, since the only anticipated user of this API requires CAPP DMA mode. Cc: Philippe Bergheaud <felix@linux.vnet.ibm.com> Signed-off-by: NIan Munsie <imunsie@au1.ibm.com> Reviewed-by: NAndrew Donnellan <andrew.donnellan@au1.ibm.com> Reviewed-by: NFrederic Barrat <fbarrat@linux.vnet.ibm.com> Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>
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