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[78.94.0.50]) by smtp.gmail.com with ESMTPSA id t82sm5764991wmf.22.2021.06.23.05.17.54 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 23 Jun 2021 05:17:55 -0700 (PDT) Subject: Re: [PATCH] firmware: export x86_64 platform flash bios region via sysfs To: David Laight , "akpm@linux-foundation.org" Cc: "linux-kernel@vger.kernel.org" , "philipp.deppenwiese@immu.ne" , "gregkh@linuxfoundation.org" References: <20210622142334.14883-1-hans-gert.dahmen@immu.ne> <5ee9e467bfbf49d29cb54679d2dce1c3@AcuMS.aculab.com> From: Hans-Gert Dahmen Message-ID: Date: Wed, 23 Jun 2021 14:17:54 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <5ee9e467bfbf49d29cb54679d2dce1c3@AcuMS.aculab.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, these are some good points. On 23.06.21 00:18, David Laight wrote: > Are you saying that my 15 year old 64bit Athlon cpu and bios > have this large SPI flash No. The reads will wrap, i.e. if your flash is 2MB then it would be repeated 8 times in the 16MB window. > and the required hardware to > convert bus cycles to serial spi reads? Yes. The window is part of the DMI interface and the south bridge or PCH converts the bus cycles to SPI reads. It is because this region contains the reset vector address of your CPU and the very first instruction it executes after a reset when the internal setup is done will actually be loaded from the serial SPI bus. It is AFAIK part of AMD's original 64-bit specification. However, after reading your mail I understand that I should have looked up the exact explanations in the respective specs. So to definitively answer your question I need to know which south bridge there is in your 15 year old system and have a look into its datasheet. Do you know which one it is by any chance? Hans-Gert Dahmen