From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Kurtz Subject: Re: [PATCH 2/2] pinctrl/amd: use byte access to clear irq/wake status bits Date: Fri, 20 Jul 2018 17:38:17 -0600 Message-ID: References: <20180717005719.258905-1-djkurtz@chromium.org> <20180717005719.258905-2-djkurtz@chromium.org> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Daniel Drake Cc: Shyam-sundar.S-k@amd.com, Nehal-bakulchandra.Shah@amd.com, Ken.Xue@amd.com, Thomas Gleixner , Linus Walleij , "open list:PIN CONTROL SUBSYSTEM" , linux-kernel@vger.kernel.org List-Id: linux-gpio@vger.kernel.org Hi Daniel, On Tue, Jul 17, 2018 at 6:30 AM Daniel Drake wrote: > > On Mon, Jul 16, 2018 at 7:57 PM, Daniel Kurtz wrote: > > Commit 6afb10267c1692 ("pinctrl/amd: fix masking of GPIO interrupts") > > changed to the clearing of interrupt status bits to a RMW in a critical > > section. This works, but is a bit overkill. > > > > The relevant interrupt/wake status bits are in the Most Significant Byte > > of a 32-bit word. These two are the only write-able bits in this byte. > > I don't have the hardware to test this any more, and I also don't have > any docs to double if those are really the only writable bits, but > looking at the existing driver code it does seem to be the case. > > I think you should retain the comment noting that the value of the > register may have changed since it was read just a few lines above > (and hence explaining more precisely why we make the special effort > just to modify the MSB), just in case there is further rework of this > code in future and we end up walking into the same trap. It was one of > those issues that took a frustratingly long time to figure out... Sounds reasonable. How about: - /* Clear interrupt. - * We must read the pin register again, in case the - * value was changed while executing - * generic_handle_irq() above. + /* + * Write-1-to-clear irq/wake status bits in MSByte. + * All other bits in this byte are read-only. + * This avoids modifying the lower 24-bits because they may have + * changed while executing generic_handle_irq() above. */ > > Thanks > Daniel