Re: [PATCH v2] ata: libahci: clear PxCLBU and PxFBU for AHCI_HFLAG_32BIT_ONLY

[Niklas Cassel <cassel@kernel.org>]

On Fri, Sep 04, 2026 at 03:43:11PM +0200, Niklas Cassel wrote:
> A user reported that commit 105c42566a55 ("ata: ahci: force 32-bit DMA for
> JMicron JMB582/JMB585") made the JMicron JMB585 unusable on his board.
> 
> The failure is seen as soon as the ahci driver is probed, and booting with
> iommu=off does not solve the problem.
> 
> Looking at the AHCI specification, PxCLBU and PxFBU are both read only '0'
> for HBAs that do not support 64-bit addressing.
> 
> For HBAs that do support 64-bit addressing, the registers are read write,
> with a reset value that is Implementation Specific.
> 
> When using the AHCI_HFLAG_32BIT_ONLY flag, the HBA does support 64-bit
> addressing, and a 32-bit DMA mask is set by simply clearing HOST_CAP_64.
> Thus, in this case, we need to explicitly clear the registers to 0.
> 
> Fixes: 105c42566a55 ("ata: ahci: force 32-bit DMA for JMicron JMB582/JMB585")
> Fixes: c7a42156d99b ("ahci: disable 64bit dma on sb600")
> Cc: stable@vger.kernel.org
> Reported-by: Roland Waltersson <roland.waltersson@netinsight.net>
> Closes: https://lore.kernel.org/linux-ide/IA0PR17MB668730A4ECCD65F7A1DC3EDC9EB62@IA0PR17MB6687.namprd17.prod.outlook.com/
> Signed-off-by: Niklas Cassel <cassel@kernel.org>

Hello Roland,

Any chance to get a Tested-by from you?


Kind regards,
Niklas