From mboxrd@z Thu Jan 1 00:00:00 1970 From: timur@codeaurora.org (Timur Tabi) Date: Wed, 8 Feb 2017 17:04:57 -0600 Subject: [PATCH 1/2] tty: pl011: Work around QDF2400 E44 stuck BUSY bit In-Reply-To: <6afb0a98-0973-33ec-0b76-fc6378e64309@codeaurora.org> References: <20170208005736.18724-1-cov@codeaurora.org> <6afb0a98-0973-33ec-0b76-fc6378e64309@codeaurora.org> Message-ID: <5e18324f-d09d-d652-df23-d4a3f8f053fd@codeaurora.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 02/08/2017 04:22 PM, Christopher Covington wrote: >>> >> - while (pl011_read(uap, REG_FR) & uap->vendor->fr_busy) >>> >> + while ((pl011_read(uap, REG_FR) ^ uap->vendor->inv_fr) >>> >> + & uap->vendor->fr_busy) >> > >> > I really think the XOR logic needs to be documented wherever it's >> > used. It's just too confusing. > References such as the following for basic bit operations like > setting, clearing, and toggling are easy enough to come by. > > http://stackoverflow.com/questions/47981/how-do-you-set-clear-and-toggle-a-single-bit-in-c-c I know what XOR does. I was thinking a more high-level comment would be appropriate. With E44, we want to ignore the BUSY bit and use TXFE instead. So was hoping to a comment that says that: /* Normally, we poll until BUSY=0, but E44 says we should poll until TXFE=1 instead. So with E44, we set fr_busy to TXFE, but we have to invert it. */ -- Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc. Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.